Cook Pasta – Bring a pot of salted water to boil, cook pasta until al dente. Reserve ½ cup pasta water, then drain.
Make Garlic Butter Sauce – In a large skillet, melt butter with olive oil over medium heat. Add minced garlic and sauté 1–2 minutes until fragrant (do not brown). Stir in red pepper flakes if desired.
Combine – Toss cooked pasta in the skillet with garlic butter sauce. Add a splash of reserved pasta water to coat evenly.
Finish – Stir in Parmesan cheese, parsley, and lemon juice if using. Season with salt and black pepper.
Serve – Plate warm and garnish with extra Parmesan or parsley.