Boil salted water. Add angel hair pasta.
Cook 2 to 3 minutes until al dente. Do not overcook.
Reserve 1 cup pasta water. Drain pasta. Set aside.
While pasta cooks, melt butter in large skillet over medium heat.
Add garlic once butter foams.
Cook 1 to 2 minutes until golden. Stir constantly.
Add ½ cup pasta water. Swirl to combine.
Add pasta to skillet. Toss to coat.
Add Parmesan, parsley, salt, pepper, and red pepper flakes.
Toss together. Cheese will melt and create silky sauce.
Add more pasta water if too thick.
Add lemon juice if using. Toss once more.
Remove from heat. Serve hot.
Garnish with Parmesan, parsley, and lemon wedges.