Heat the olive oil over medium-high heat in a small saucepan. Add the onion and saute until translucent. Add the garlic and saute until fragrant. Turn off the heat.
Add the sauteed veggies to a blender along with the cashews, nutritional yeast, Dijon, and plant milk. Blend until smooth.
Taste the sauce and blend in additional salt and pepper to taste.
Make the pasta:
Bring a large pot of water to a boil and add the salt. Add the pasta and boil per the package’s instructions until al dente. Scoop 2 cups of pasta water out of the pot and drain the pasta.
While the pasta is boiling, melt the vegan butter over medium heat in a large, heavy-bottomed saucepan. Add the mushrooms and season with salt and pepper. Saute until softened and nicely caramelized.
Add the pasta to the pan with the mushrooms. Reduce the heat to low and add the sauce. Toss until the sauce has thoroughly coated every strand of pasta. Add some of the reserved pasta water as needed if the sauce is too thick.
Serve warm, garnished with fresh parsley.
Notes
To store: Store leftover pasta carbonara in an airtight container; you can keep it in the refrigerator for up to 3-4 days. When you're ready to enjoy the leftovers, simply reheat them in a skillet over medium heat or in the microwave, adding a splash of plant milk to loosen up the sauce.To freeze: For longer storage, you can freeze pasta carbonara in an airtight container or freezer bag for up to 3 months. Thaw in the refrigerator overnight before reheating for the best results.