Cook the spaghetti according to package directions in a large pot of salted water until al dente. Before draining, reserve about 1 cup of the starchy pasta water. Drain the spaghetti and set aside.

While the pasta is cooking, heat the olive oil in a large skillet or Dutch oven over medium heat. Add the minced garlic and cook for 1-2 minutes until fragrant, being careful not to brown it.

Add the butter to the skillet and let it melt completely. Stir in the heavy cream and bring the mixture to a gentle simmer, stirring occasionally. Reduce heat to low.

Gradually whisk in the grated Parmesan cheese until it's fully melted and the sauce is smooth and creamy. If the sauce is too thick, add a splash of the reserved pasta water to reach your desired consistency.

Add the drained spaghetti to the skillet with the sauce. Toss well to coat the pasta evenly. If the sauce seems too thick, add more reserved pasta water, one tablespoon at a time, until the spaghetti is perfectly coated.

Season with salt, freshly ground black pepper, and optional red pepper flakes to taste. Garnish with fresh chopped parsley and additional grated Parmesan cheese before serving immediately.