Bring a large pot of salted water to a boil, then add pasta and cook until al dente.

Before draining, reserve about 1 to 1.5 cups of the starchy pasta cooking water.

While pasta cooks, melt butter in a large skillet over medium-low heat.

Add minced garlic to the melted butter and sauté gently for 1-2 minutes until fragrant, being careful not to brown or burn it.

If using, add red pepper flakes now and cook for another 30 seconds.

Ladle in about 1/2 cup of the reserved pasta cooking water into the skillet; bring to a gentle simmer, stirring to combine with the butter and garlic to create a slightly thickened sauce.

Transfer the cooked pasta directly into the skillet with the garlic butter sauce.

Add grated Parmesan cheese and chopped parsley, then toss everything vigorously for 1-2 minutes until the pasta absorbs the sauce, adding more pasta water if too thick.

Season with salt and pepper to taste and serve immediately, garnished with extra Parmesan and parsley if desired.