Cook the pasta in a pot of salted water according to package instructions until al dente. Drain, reserving 1 ½ cup of the cooking pasta liquid.

In a large skillet over medium heat, heat the olive oil. Add the onions and cook until soft, about 5 minutes. Add the garlic and cook until fragrant, about 1 more minute.

Transfer the thawed peas to the skillet, saving a couple tablespoons for serving. Add the basil and 1 cup pasta water. Bring sauce to a simmer for 10 minutes.

Use an immersion blender to blend the sauce until it’s smooth and consistent. Use a strainer to strain the sauce or an extra creamy consistency.

Transfer the cooked pasta to the skillet with the peas sauce, salt and pepper and toss until well coated. Add as much of the extra ½ cup reserved pasta water as desired to thin out the sauce.

Add the reserved whole peas, parmesan cheese and stir until everything is well combined. Serve with fresh basil, if desired.