Lemony Asparagus Pasta

Bring a large pot of salted water to a boil. Add penne and cook according to package directions, until al dente. Reserve ½ cup pasta water, then drain. Set aside. Meanwhile, in a large skillet over medium-high heat, heat 1 tablespoon oil. Cook asparagus until crispy, then season with pinch of salt. Transfer to a plate and set aside.  Heat remaining 2 tablespoons oil over medium heat. Cook onions and garlic until softened, about 5 minutes. Add heavy cream, white wine, lemon juice, and zest. Bring mixture to a boil, then simmer for 5 minutes. Add in salt, Parmesan, and black pepper. Reduce heat to low and mix until well combined.  Turn off heat and mix in pasta, asparagus, and parsley until well coated. Add small amounts of pasta water until you reach desired consistency. Serve with more grated Parmesan, cracked black pepper, and red pepper flakes.