Soak the cashews. Cover cashews with hot water and let sit for 20–30 minutes. Drain before blending. If you’re short on time, simmer them for 10 minutes instead.

Boil the pasta. Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente.

Add the broccoli. In the last 2–3 minutes of pasta cooking, add the broccoli florets to the pot. Cook until bright green and just tender. Reserve 1 cup of pasta water, then drain.

Blend the sauce. In a blender, combine soaked cashews, oat milk, nutritional yeast, garlic, lemon zest, lemon juice, olive oil, salt, pepper, and onion powder. Blend until completely smooth and creamy.

Thicken (optional). For a thicker sauce, blend in cornstarch. Alternatively, whisk 1 tablespoon cornstarch with 2 tablespoons cold water, then add to the sauce in the pan in the next step.

Warm the sauce. Pour the sauce into the empty pasta pot. Cook over low heat for 2–3 minutes, stirring, until it gently thickens. If it gets too thick, loosen with a splash of reserved pasta water.

Toss it all together. Add the drained pasta and broccoli to the pot. Toss until coated and glossy. Adjust seasoning with extra salt, pepper, and lemon juice. Add red pepper flakes if you like heat.

Finish and serve. Garnish with chopped parsley and more nutritional yeast if desired. Serve hot.