Make the cashew cheese for the risotto by blending together the cashews and the miso with enough water to make a smooth paste. If you don't have miso you could use 2 tbsp nutritional yeast, or leave it out altogether and just use the cashew paste.
Heat 1 tsp of oil in a saucepan.
Add the chopped onion, season with some salt, red pepper flakes and ground black pepper and saute until softened, about three to four minutes.
Add the garlic, saute for a few seconds, then add the mushrooms and white wine.
Turn up the flame to medium-high and cook until the wine has evaporated and the mushrooms have taken on a nice sheen.
Add the black rice, season with more salt and pepper to taste, and saute for a minute. Now add 1/2 cup of water and let it cook until the water evaporates, stirring frequently. Just before the rice dries completely, add another 1/2 cup of water. Repeat, stirring the risotto frequently, until the rice is cooked but still has a bite to it. This process takes some time, so be patient.
Now add the cashew cheese and mix well. The risotto should have a creamy, slightly soupy consistency when done. Add more salt if needed.
Now heat the remaining 2 tsp of oil in another saucepan, add the sliced onions and sugar with a pinch of salt, and saute, stirring frequently, until the onions turn golden brown.
Top the risotto with the caramelized onions and serve hot.