Cook your pasta in salted water according to package directions, making sure to save about 1/3 cup of the pasta water. In a pan over medium heat, add butter, onion, and garlic. Cook until softened, about 2 minutes. Add the tomato paste and cook until lightly caramelized. Stir in the heavy cream, then season with salt and pepper to taste. Add the Parmesan cheese, reserved pasta water, and your cooked pasta to the pan. Mix everything well to combine and coat the pasta. Serve immediately, garnished with fresh basil or additional Parmesan cheese.
