Cook the onions: Heat a large non-stick pot over medium-high heat for one minute and add onions. Sauté for 3 to 4 minutes until they start to soften, adding 1 tablespoon of water at a time if they start to stick.
Cook the mushrooms: Add the mushrooms, nutritional yeast, and dried herbs/spices and cook for 5 to 7 minutes until they have released most of their water.
Add pasta and stock: Add the dry pasta and 2 cups of the unsalted vegetable stock or broth to start and stir well. Push all the pasta down so it’s been moistened by the liquid.
Cook the pasta: Lower the heat to medium, place a lid on the pot but tilt it so it let's some air through, and cook the pasta for 5 to 7 minutes until the pasta is al dente, stirring occasionally and removing the lid halfway through so that the excess liquid can evaporate, and pushing the pasta back down every time you stir. If the pasta has absorbed all of the liquid but isn't cooked yet, you can add a quarter to a half cup more stock (or water), but don't add too much.
Make the cream sauce: Add the white beans, soy milk (or any unsweetened plant-based milk), lemon juice, and miso paste to a blender. Blend until smooth. You may need to stop and scrape down the blender and re-blend since it's a small batch. You could also double it if you want a really saucy mushroom stroganoff.
Troubleshooting: If there's too much liquid in the pot and the pasta is cooked, use oven mitts to carefully spill the excess liquid out. Use one hand to hold the lid slightly ajar so you can spill out some of the excess cooking liquid. You can dump it into a colander, but I like to keep some of that liquid for the sauce. You could also make a cornstarch or arrowroot powder slurry by mixing one tablespoon of the starch with 2-3 tablespoons of water and stirring it really well, then stirring it into the pasta and cook over medium heat for a few minutes until it thickens.
Make it creamy: Use a blender spatula if you have one to scrape out as much of the blended cream sauce as possible, stir, and heat for a few minutes.
Finish up: Remove from heat and stir the parsley. Taste and add any additional lemon juice, thinned miso, black pepper, etc. If the sauce is only slightly too thin, you can either spill out some of the liquid (see step 6) or you can add some nutritional yeast or dehydrated potato flakes to thicken it.
Serve: Serve immediately and enjoy. I like to serve this with a large side of vegetables or a side salad.
Storage: Let the vegan mushroom stroganoff cool to room temperature and store in an airtight container in the refrigerator for up to 5 days. Reheat gently in the microwave or over low heat in a pot on the stove. Add a splash of unsweetened plant-based milk if needed.