Sweet mashed chestnut and sweet potato

Properly speaking, kuri-kinton (a sweetened chestnut confection) should have its whole coating made from nothing but chestnuts, but making it that way takes a tremendous amount of work. You steam the chestnuts, peel off the hard outer shell (oni-kawa), peel off the astringent inner skin (shibukawa), soak them in alum water, and then steep them in syrup. On top of that, it costs roughly ten times as much as sweet potato, so you can't use all-chestnut kinton in a jūbako box that sells for around 10,000 yen — which is why the lower-cost sweet potato is used for the coating instead. A coating made purely from chestnut has a completely different, genuinely delicious moistness. How close you can bring the sweet potato to that is what really determines the outcome.

For the kinton coating, first peel the kuri-kintoki (a sweet-potato variety) and slice it thinly into rounds. Sweet potato has a lot of fiber, and unless you peel away the fibrous layer around the outside as well, bitterness spreads through the flesh, so peel it fairly thick. Also, the fibers reach in fairly deep, so peeling alone will always leave some fiber behind, which is why you finish it with a knife. Slice the rounds as thin as possible so heat penetrates evenly, and since differences in thickness lead to uneven boiling, keep the thickness and size as consistent as you can.

If you leave the peeled or sliced potato sitting out, it will pick up bitterness on contact with air, so peel about 3 or 4 potatoes at a time, slice them into rounds right away, put them into water, and let them soak overnight like that. The parts most prone to picking up bitterness are the two ends of the potato, where the fiber is denser, so those parts are trimmed away and not used for the kinton. Of course, they're not thrown away — they get used in a separate preparation — so you don't need to worry too much about wasting the ends. In terms of quantity, each potato is about 70 to 80 g. Since 20 to 30 percent of that is peeled away, what's actually used works out to about 40 to 50 g.

Boil the sweet potato after it's been soaked in water. First, boil it to draw out the bitterness, add color with gardenia fruit (kuchinashi), and then boil it properly and thoroughly. When boiling it, divide the whole batch into three portions so that the conditions in the pot stay as consistent as possible each time. If you pile it up too high in the pot, the heat won't penetrate evenly, so you divide it into three portions, each loose enough to cook properly.

First, put it into boiling water to draw out the starch-related bitterness. Unless a certain amount of the starch in the potato washes away, an unwanted stickiness will remain once it becomes kinton. Since it will be boiled properly again later, it's fine if it's a bit firm at this stage. It depends on the particular potatoes, but in this case it takes roughly eight minutes. Once the bitterness has been drawn out, transfer it to a pot of water with gardenia fruit added. The reason for using gardenia fruit is that kintoki sweet potato is used here, and its color is a bit pale, so this adds a touch of color — you lift it out once the color has shifted just slightly. Since it's called 'kinton' ('golden dumpling') because of its golden color, there are really only two types of kinton: a golden-yellow one that looks properly gold, and a platinum-white one that looks properly pale — I want to be particular about the color either way. As a side note, coloring isn't just about adding color for its own sake — every one of these has a purpose. Safflower, for instance, is used for dyeing, but even after being exposed to the cold-bleaching process, it doesn't chap the hands. That's because it's a medicinal herb that's good for the skin, and in the same way, it also functions as a preservative. That's how it ends up serving as a preservation method, or providing an antibacterial effect. That's exactly why ingredients like this are used — it's the wisdom of those who came before us.

Even when you carry out the process the same way each time, some pieces end up with slightly softer fiber, and there's no way to judge that with total precision, so some pieces will inevitably break apart a little as they finish boiling. Since it gets pressed through a sieve afterward anyway, it's fine if the potato breaks apart somewhat at this stage.

Once it's boiled, put it into a pot and add sugar. Since you'll be working from multiple pots' worth of boiled potato, you first measure out and decide, relative to the amount of potato in each pot, roughly how much sugar you'll use when working it in. You can't add all the sugar at once from the start. Unlike salt, sugar melts and turns watery when heated, so if you add it all while cooking and working the mixture, it tends to turn into a hard candy. To let it blend in gradually, you add only a certain portion at first, and since the rest goes in later, you label the wrapped remainder with numbers so you know exactly how much sugar is left. What you add first is roughly one third of the total — any more than that, and it turns watery instead. So, first pass: tap it in gently, bit by bit, working the sugar into the potato. Once the sugar and sweet potato have blended together to a certain degree, lightly mash it with a pestle to make it easier to pass through a sieve, and then press it through. From boiling, through mashing, to pressing it through the sieve, you carry it all out as one continuous flow of work so it doesn't cool down. Once sugar cools, it hardens, so it stops blending in properly and you can no longer press it through.

To bring the flavor of the sweet potato closer to that of chestnut — to erase its raw potato smell and match it to chestnut's sweetness — you soak the potato thoroughly in water and combine it with sugar. Also, sweet potato has stronger fiber than chestnut does, so unless you sieve it very thoroughly, the fiber gets tangled in and the mixture never achieves a unified texture. So, to keep it from tasting bluntly like 'sweet potato kinton' the moment it hits the mouth, and to make the coating resemble sieved chestnut as closely as possible, you press it through the finest possible sieve mesh, finishing it into a quite creamy consistency. There probably aren't many other places that sieve it this thoroughly.

Combine sake and honey into the sieved mixture, and then put it over heat. Before putting it over heat, work it together well one more time first. Sugar and potato both have a tendency to seize up on their own, so if you don't combine them thoroughly and properly at this point, they won't blend, and once it's over heat, they'll fail to mix well and separate into layers instead. The reason for adding the honey first is that, without a certain amount of moisture present, the potato will suddenly seize up the moment it hits the heat — so to let the heat spread through the whole mixture evenly, you add a certain amount of moisture, putting in whatever releases moisture first. This is also what removes the raw potato smell. You can't cook it through properly without adding moisture, but adding water would risk spoilage, so sake is used instead, and the alcohol content cooks off while it's over the heat. The heat shouldn't be too strong, either. The key point at the working stage is that if you work it over too low a heat at first, only the moisture evaporates off, so you apply somewhat higher heat to begin with, to a certain degree. Because sugar is already in the mixture, unless you apply a certain amount of heat fairly early on, only the moisture will evaporate and it will turn into something like hard candy, mixing poorly. So you work it over fairly high heat up to a point, and once it's cooked through, you bring the heat back down a bit, get the texture completely right, and then, watching its condition, add the remaining sugar and keep working it. If you add sugar while it's still over the heat, lumps will form, so take it off the heat once before mixing it in. You can't add it too many times, so you divide it into two or three additions, adding it in a way that keeps it from reducing down into hard candy. These days, the mainstream approach is to keep the sugar as restrained as possible. Sugar does serve as a preservative for keeping quality, so there's nothing wrong with using a lot of it, but in our case, following the recent trend, we hold the sweetness back and use the bare minimum amount of sugar that still keeps the dish shelf-stable.

How long you work it depends on the heat level, but you work it to a certain point, and as a rough gauge, you draw a single line across the bottom of the pot with a Miyajima paddle (a rice-paddle-shaped tool, named for the famous shamoji made on the island of Miyajima) and judge whether it's done by how firm the potato is as it flows back in from either side — but that's really something you sense by feel, so I can't quite tell you it takes so many minutes. Right before adding the chestnuts, you add just the faintest amount of salt to bring out the sweetness.

Combine the finished coating with the chestnuts. The chestnuts are ones that were preserved in syrup back in the fall. When you combine them, unless the potato coating and the chestnuts are brought to the same temperature, they won't blend properly, and layers will form with moisture leaking out. When combining in the chestnuts, mirin and water-based starch syrup (mizuame) are added together with them, both to bring out a glossy sheen and to keep the mixture from drying out. Mirin has a tendency to set firm, so you can't add much of it from the very start, but once the mixture has loosened up to a certain degree, you use the mirin to firm it up just slightly. At this point, you do what's called oka-maze once — mixing it together without applying heat, to let it blend first — and then, to bring the coating and chestnuts together as one, you gradually apply heat from below in stages, blending it in as you go. Western cooking is built around high, direct flame, so Western pots aren't designed to use their rim edges, but Japanese pots are based on the yukihira-nabe style, so the whole rim can be used. This step matters a great deal: working it over the gas burner using the pot's rim, tilting the pot at an angle, turns the mixture soft like mochi and lets it peel away cleanly from the pot. Then you fold over the part that's dropped down, turning the pot little by little, bringing the whole mixture together. Once you've added the chestnuts, you can no longer use the Miyajima paddle, since it would break them apart. From that point on, it's purely a matter of heat control, folding and finishing the mixture by turning the pot. In the old days, so much sugar was used to firm it up that the mixture would barely peel away from the pot at all, but these days the sugar amount is kept relatively low, so it stays softer, and as a result, the working time has also been shortened compared to before.