Wagashi- traditional Japanese confectionery- tends to be an elegant and artistic representation of the season. As we’ve recently passed the equinox and the cooler nights are starting to extend, nature is gradually turning from green to red and it’s time to embrace the change and eat something a little more Autumnal. Alongside kabocha, mushrooms and persimmons, sweet potatoes are one of the key flavours that the Japanese look forward to eating during shokuyoku no aki or ‘the increased appetite of autumn’ and one of most popular ways to enjoy them is as a smooth, firm bar of imo yōkan.
Yōkan is one of the oldest forms of sweet still eaten regularly across Japan and is essentially a block of jellied mashed azuki beans, or in this case, mashed sweet potatoes. We’ve enhanced our yōkan further with the addition of pieces of intense, almost chestnut-tasting, candied sweet potato to exaggerate the earthy, woodland flavour and add an extra texture to the jelly. This delicately coloured, refreshing treat is the perfect accompaniment to a cup of matcha both in looks and taste, the sweet gel coating your mouth, balancing and rounding out the bitterness of the tea.
- 475g sweet potato
- 3g kanten (agar agar) powder
- 280g caster sugar
- 1 tablespoon rice vinegar
- pinch of salt
- Peel the sweet potatoes and slice them into 2cm thick discs; reserve 75g to use for making the candied sweet potato, then add the remaining slices to a bowl of cold water deep enough to cover the potatoes well and add one tablespoon of rice vinegar to the water. Leave the potatoes to soak for around an hour- this helps to remove excess starch from the sweet potato, and the vinegar prevents it from becoming discoloured whilst also adding to the flavour of the finished yōkan.
- Make the syrup for the candied sweet potato by adding 250ml water to a medium saucepan with 200g of the caster sugar; bring the liquid to a simmer slowly over a low heat, swirling the pan to make sure all the sugar dissolves; resist the temptation to stir until everything has dissolved as it can make the sugar recrystallize. Cook the syrup until it is slightly thickened but not coloured.
- While the syrup is bubbling away, chop the reserved sweet potato slices into small chunks and add them to the pan. Let the potatoes simmer for five minutes before turning off the heat and leaving the syrup to cool down- the residual heat should be enough to cook the small pieces through.
- Drain and rinse the soaked sweet potato slices, then place them in a steamer basket and steam over boiling water for fifteen to twenty minutes, until tender. When cooked, mash the potatoes roughly and mix in 250ml cold water, blend the mixture with a stick blender until smooth then strain through a fine sieve into a medium saucepan. Add the kanten powder, pinch of salt and the remaining 80g sugar then cook over a low heat until the sugar has dissolved, everything is well combined and the paste is starting to thicken slightly (the yōkan mixture will burn quite easily at this point, so be sure to stir it constantly).
- Remove the candied sweet potato pieces from their syrup and gently dry them on a piece of kitchen roll before stirring them into the yōkan; take the pan off the heat and let it rest for three or four minutes. Pour the mixture into a rectangular or square glass dish, smooth the top with a spatula if necessary, then leave in a cool place to set- this will only take two to three hours, but we like to leave it overnight to be certain that it’s firm.
- Run the tip of a sharp knife around the edge of the yōkan to loosen it, place a chopping board over the top of the dish and flip it over to unmould the jelly (if it doesn’t immediately drop onto the board, just give gravity a little time to work its magic). Cut the yōkan into bite-sized pieces and serve, ideally with a cup of green tea after a meal or as a mid-morning snack.
Serves 6-8 people.