Bring 4 quarts water to a boil in large pot, add 2 tablespoons salt.
Add 1 pound spaghetti, stir. Cook 8-10 minutes until al dente. Reserve 1 cup pasta water.
Drain spaghetti.
Heat 1/4 cup olive oil in skillet over medium. Add 6 minced garlic cloves and red pepper flakes. Sauté 1-2 minutes until fragrant.
Toss drained spaghetti in garlic oil. Add 1/2 cup reserved pasta water, adjust as needed.
Stir in 1/4 cup parsley and 1/4 cup Parmesan. Season with salt and pepper.
Mix 1 cup softened butter, 8 minced garlic cloves, 1/4 cup parsley, 1/4 cup Parmesan, garlic powder, salt, pepper.
Slice Italian bread lengthwise.
Spread garlic butter on cut sides.
Preheat oven to 375°F (190°C). Bake bread cut-side up 10-12 minutes until golden. Broil 1-2 minutes if desired.
Slice bread. Serve with spaghetti, extra Parmesan.