Bring a large pot of water to a rolling boil and add a generous amount of salt. Add spaghetti and cook for 8-10 minutes until al dente; reserve 1 cup of pasta water before draining.

In a large sauté pan over medium heat, melt the unsalted butter. Add the minced garlic and cook for 1-2 minutes until fragrant and lightly golden.

Drain the spaghetti and transfer to the sauté pan with garlic butter. Pour in 1/4 cup reserved pasta water and toss for 1-2 minutes to emulsify the sauce.

Reduce heat to low, add the grated Parmesan, and stir until melted. Adjust seasoning with salt and black pepper.

Remove from heat, fold in chopped parsley, serve in bowls, and add extra Parmesan if desired.