Bring a large pot of salted water to a boil. Add spaghetti and cook according to package instructions until al dente. Reserve about 1 cup of pasta water, then drain the rest.

In a large skillet, melt the butter over medium heat. Add the minced garlic and sauté for about 1-2 minutes until golden and fragrant—avoid burning!

Add the drained pasta to the skillet. Toss the pasta in the garlic butter. Gradually add reserved pasta water for moisture as needed.

Remove from heat and stir in the grated Parmesan cheese. Toss until well combined and creamy, adjusting seasonings with salt, pepper, and optional chili flakes or lemon zest if using.