Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Drain and set aside.
While the pasta cooks, heat 2 tablespoons of butter in a large skillet over medium heat until melted.
Add the minced garlic and red pepper flakes to the skillet and sauté for about 1 minute until fragrant, stirring frequently to prevent burning.
Add the shrimp to the skillet, season with salt and black pepper, and cook for 2-3 minutes on each side until the shrimp turn pink and are cooked through. Remove the shrimp from the skillet and set aside.
Pour the chicken broth into the same skillet and bring to a simmer. Let it reduce slightly for about 2 minutes.
Add the remaining 2 tablespoons of butter to the skillet and stir until melted and the sauce is smooth.
Return the cooked shrimp to the skillet and toss to coat in the garlic butter sauce.
Add the cooked penne pasta to the skillet and toss everything together until the pasta is well coated with the sauce.
Remove the skillet from heat and stir in the grated Parmesan cheese and chopped fresh parsley.
Serve immediately, garnished with additional Parmesan cheese and parsley if desired.