While the pasta cooks, saute onion in 2 Tbsp butter or oil with 1 tsp of salt until soft.
Add in minced garlic and saute for an additional 2 minutes.
In a blender, pour in the hot onion and garlic, milk, nutritional yeast, and tomato paste. Blend until fully combined. You could also use a stick blender for this!
Heat mixture over medium low heat until hot.
While sauce is heating, saute the mushrooms in the other 2 Tbsp butter or oil with a touch of salt, until browned.
Toss the pasta with the sauce and mushrooms, garnish with parsley.
Notes
Variations:Gluten-free - use brown rice or corn pastaKeto/grain-free - use zucchini noodles