Boil 6 cups of water in a large pot set over high heat and salt generously. Add the pasta and cook according to the package until al dente.
1 pound dry pasta
While the pasta cooks, heat the butter and olive oil together in a large skillet set over medium-high heat. Add the asparagus and garlic. Stir and cook until the asparagus starts to soften, about 3 minutes.
Pour in one cup of the pasta water. Add the heavy cream, lemon juice, red pepper flakes, salt, and pepper and let it cook down until the pasta is ready.
½ cup heavy cream, 1 lemon, ½ teaspoon crushed red pepper flakes, ½ teaspoon kosher salt, ½ teaspoon ground black pepper
Drain the pasta and add it to the skillet. Toss to combine and sprinkle with Parmesan cheese. Serve with fresh parsley and lemon wedges.