Uni (sea urchin) is really an amazing ingredient. It's great on its own and it also has so many other uses. You can dehydrate dried uni and put it in a food processor or blender to make a powder that tastes like cheese. I make a compound butter from pureed raw fresh uni for a umami-heavy finish to this risotto. Instead of the traditional white wine and stock, the risotto is cooked in dashi and deglazed with sake for an Eastern take on the Italian classic. The uni gives it a cheesy flavor that you would get from an Italian risotto finished with Parmesan.
Puree the uni in a food processor until smooth. In a large bowl, combine half of the pureed uni and half of the butter and incorporate using a rubber spatula. Gradually add the remaining butter and uni until all of the uni is incorporated and no liquid is left. Cover and freeze for up to 1 year.(
Soak the kombu in 9 cups cold water in a large pot for 20 minutes. Place the pot over medium heat and heat until small bubbles begin to break on the surface of the water at the edge of the pot. Add the bonito flakes, scattering them across the surface of the water, and the shiitakes (if using). Let sit for 3 to 4 minutes, then strain. Makes 2 quarts.
Place a large, deep skillet over medium heat and drizzle with the olive oil. Add the shallot, garlic, and a small pinch of the yukari salt. Cook until translucent, about 3 minutes.
Add the rice and stir for a minute or 2 with a wooden spoon until the grains are well coated and opaque. Add another pinch of the yukari salt. Stir in the sake and cook for about 2 minutes to allow the alcohol to burn off. Pour in 1 1/2 cups of the hot dashi. Stir with the wooden spoon until the rice has absorbed all of the liquid. Continue adding dashi, 1 cup at a time, allowing the rice to absorb the liquid before adding the next cup. Continue this process until the risotto is loose and the rice grains are just cooked but still toothsome and suspended in the thick creamy sauce, about 20 minutes.
Stir in the uni butter until melted and incorporated, then stir in the chopped shiso.