Add 3/4 cup cashews (90 g // adjust amount if altering batch size) to a bowl and cover with at least 2 inches of water. Set aside to soak.
For the pasta, bring a large pot of well-salted water to a boil.
Heat a large rimmed skillet (or large pot) over medium heat. Add olive oil and onions and cook until tender — about 4-5 minutes. Add garlic and red pepper flakes and continue cooking until fragrant — about 30 seconds.
Add crushed tomatoes, tomato paste, and salt and bring to a simmer. Reduce heat to low, cover, and continue simmering for 10 minutes or until thickened.
When the pasta water is boiling, add the pasta and stir to prevent clumps. Cook to al dente according to package instructions. Reserve 1/2 cup (120 ml) of pasta water and drain the pasta.
Drain cashews and add them to a high-speed blender with nutritional yeast and 1 cup (240 ml // adjust amount if altering batch size) of water. Blend until smooth and creamy.
To the tomato sauce, add cashew mixture and stir to combine. Add reserved pasta water a little at a time until it becomes a thick but pourable sauce. Taste and adjust, adding more tomato paste for tomato flavor, nutritional yeast for cheesiness, red pepper flakes for heat, or salt for overall flavor.
Add drained pasta to the sauce and stir to coat. It should be quite saucy and well coated. Serve warm and garnish with fresh basil and vegan parmesan cheese (optional).
Leftovers will keep in a sealed container in the refrigerator up to 3-4 days. Sauce can be frozen up to 1 month.
*If cashew-free, you can sub full-fat coconut milk for the cashews and water, but sauce will have a slight coconut flavor. *Adapted from Female Foodie. *Nutrition information is a rough estimate calculated with 12 ounces rice-based gluten-free penne and 1/4 tsp salt in the pasta water (since the full tablespoon isn’t absorbed into the pasta), and without optional ingredients.