18 Nov 2010

Double-Spud Gratin with a Sake Kasu Sauce

This is a kind of two birds with one stone thing: having rediscovered the joys of potatoes (!) whilst back in Blighty I've been itching to post a spud recipe (twice-baked jackets, for example, or cottage pie with carrot and potato mash - there's nought like hearty British potato cuisine!). Mizuki, meanwhile, has been experimenting with sake kasu (the lees left over from the sake-making process, but more on that anon), so I basically went with a recipe that combines the two. 

Sake kasu, or rice mash - the sediment that's left after the sake is pressed, comes in cakes or sheets that are packed with sake flavour and alive with bacteria and yeast. It has the texture of a soft cheese and can be eaten as is, though the taste is fruity and it obviously carries the sake flavor; it has quite a pronounced fragrance, too. It's used in home cooking here to create wonderfully complex flavored dishes during the winter sake brewing season when it's a common sight in the chilled section of the supermarket. Unsurprisingly, given all the bacteria in there, sake kasu is mainly used for marinading and pickling and it imparts a unique and highly pungent flavor, though it's beginning to appear in more untraditional forms too - Swiss rolls, sweet breads and the like. 

As to the spuds, since there are literally thousands of different varieties of potatoes grown around the world (some 80 different varieties are grown in the UK alone) and as many ways of cooking them, I've gone with Japanese varieties to compliment the sake kasu in the Bechamel sauce. The tiny, soft, furry-skinned satoimo or "village potatoes" (taro root, to you and me), which were a regional staple before rice become predominant and are usually served steamed (when they're fabulous topped with a herby salt) or in nimono (the stewed dishes that are a standard meal-time fixture during the cold winter months); and the long, beige, almost skinless tuber, nagaimo - the Japanese mountain yam, which may be eaten raw, grated, but is also amazing as part of a dish of roasted vegetables and makes a mean white sauce when steamed and combined with soy milk and miso, which is basically what I've done here, except I've used sake kasu instead of nagaimo to thicken the sauce. Both these tubers are slippery and slimy when raw (a quality that's prized in this country) and have a soft, gooey texture when steamed, boiled or roasted, though in this dish I've worked to give them different texture profiles so as to add some variety to the chew, steaming the satoimo and sauteing the nagaimo in olive oil for melt-in-the-mouth softness combined with a healthy crunch. 

Double-Spud Gratin with a Sake Kasu Sauce
(Serves 2)

6 satoimo
180g nagaimo
5-6 shiitkake mushrooms, destalked and cut in half
2 tbsp olive oil
1 clove garlic, crushed
Salt and cracked pepper
Fresh thyme to garnish

1 cup (200 ml) soy milk (unadulterated)
50g sake kasu
1.5 tbsp miso (preferably white)
a couple of pinches of salt
1/2 tbsp rice vinegar

Scrub the satoimo with a vegetable brush to remove any dirt caught in the hairy bits, then steam for about 20 minutes until soft, and remove the skin. Remove any extraneous hairy bits from the nagaimo, then cut into 1-cm slices. Heat a tablespoon of olive oil over a medium flame and saute the nagaimo until bronzed on both sides. Remove from the pan and then saute the shiitake mushrooms and set aside. Arrange the potatoes and the mushrooms in individual oven-proof gratin dishes.
Add another tablespoon of olive oil to the pan and gently fry the garlic. Pour in the soy milk and bring to a simmer, then turn off the heat. Add the sake kasu, torn into pieces, and allow to sit for 10 minutes to soften. Add the miso and the salt and stir well to dissolve all the ingredients. Heat gently to allow the sauce to thicken, then stir in the rice vinegar.
Pour the sauce over the potatoes and mushrooms and bake at 250 degrees Centigrade for 10-15 minutes until the gratin is bubbling hot and the sauce has turned the colour you want you skin to go on your summer holiday! 
Top with some thyme leaves and a good grating of fresh black pepper. 

By this time, your kitchen will be smelling like a brewery. Enjoy! The sake kasu gives this sauce an intensely fruity flavor that's unlike anything I've encountered anywhere else in the world. Not bad for the dregs of the brewing process!

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