In a large pan, heat olive oil over medium heat for about 15 seconds. Add the onions, tempeh and mushrooms and cook for 2-5 minutes. Add the garlic and mix to combine.
Bring a pot of heavily salted water to a boil and cook your pasta according to the directions.
Add the flour to the mushroom mixture and stir to combine, and add the mushroom broth and scrape all of the stuck-on bits from the bottom of the pan.
Turn the heat to medium heat and bring to a simmer. Add in the sour cream, mustard and miso paste. Stir and taste. It might need a pinch of salt and a few cranks of black pepper.
Stir in the vinegar and add your cooked pasta, saving some of the pasta water to thin the sauce out if needed. Toss until the pasta is evenly coated and dig in!