Cook the pasta in a large pot in salted water per the package instructions until al dente. (The pasta will continue to cook when added to the sauce.)
While the pasta is cooking in a large skillet over medium-low heat melt the butter. Add the garlic, sauté for 1 minute until fragrant. Next, add 1/2 of the lemon zest and lemon juice. Stir to combine and bring to a gentle simmer.
Once simmering add the heavy cream, salt, black pepper, onion powder and crushed red pepper flakes. Stir while simmering for 4-6 minutes or until the sauce has reduced slightly and begins to thicken. Taste and adjust the salt and black pepper to your taste.
To the sauce add 1/2 cup parmesan cheese, stirring until fully combined. Add the drained pasta to the skillet. Toss to fully coat the spaghetti.
Add 1/4 cup of the reserved pasta water at a time until you have the consistency you like.
Top the pasta with the remainder of the lemon zest, parmesan cheese, a sprinkling of black pepper and parsley.
Notes
Protein: You can add grilled shrimp, chicken or pork to the pasta. You could also add bacon or prosciutto to the lemon cream sauce.
Herbs: You can add fresh basil or rosemary to the pasta to expand the flavor profile.
Vegetables: You can add baby spinach, steamed broccoli, sautéed mushrooms or bell pepper and capers.