In a boiling pot of salted water cook the pasta according to the instructions on the package. Drain and set aside.
Heat the olive oil in a nonstick pan on medium heat. Add the garlic and sauté until fragrant (about 30 seconds - 1 minute). Then add the shrimp, season with salt and pepper, and sauté for 1-2 minutes.
Add the butter to the pan, once it melts stir in the flour and cook for 1 minute.
Pour in the broth and simmer, add the lemon juice and red pepper flakes (if using). Bring to a simmer for 3-4 minutes or until it thickens and the shrimp is cooked through.
Toss in the pasta and garnish with parsley; serve with crusty bread.