Melt the butter and olive oil together in a large skillet, well sprayed with cooking spray, over medium heat for about 1 minute. Add the onion and sauté, stirring often, for about 4 minutes, or until the onion begins to soften. Raise the heat slightly and add the mushroom caps. Continue cooking, stirring often, for 5 to 6 minutes more.
Pour the vegetable stock into a medium saucepan or Dutch oven, preferably nonstick, and warm over medium-low heat.
Pour the wine into a food processor and add the garlic, flour, nutritional yeast, and mustard. Buzz together to form a paste.
Whisk the paste into the warmed, but not hot, vegetable stock. Gently bring to a boil, then reduce to a simmer. Take a ladleful of this liquid and swirl it into the sautéed mushroom mixture, stirring well to scrape up any little flavorful bits from the bottom of the skillet. Add the mushrooms, onions, and liquid to the pot with the stock, scraping the sauté pan clean.
Reduce the heat to very low and let the sauce simmer very gently, stirring occasionally, for about 30 minutes. Remove from heat, place a ladelful of this liquid in a small bowl and stir in the miso until smooth. Correct the seasonings with salt (you’ll need little, if any, since miso is salty) and a lot of pepper. Serve hot, ladled over whatever good thing you are serving.
Cook noodles according to instructions on package. Drain, then spread neatly on a dry towel.
Prepare the Miso Paste by mixing those ingredients together.
Lay one eighth of the noodles side by side across one sheet of nori on which 1 tsp of the miso paste has been evenly spread. Roll up nori as firmly as possible. Repeat with remaining sheets of nori and noodles.
Using a sharp knife dampened with water, carefully slice rolls in half, then cut each half into 3 equal pieces.
Add a small amount of water at a time to wasabi, until it forms a thick paste.
Place noodle rolls along with wasabi on a platter and serve with sushi ginger slices and a dipping sauce.