Bring a large pot of water to a boil. Pour in the pasta and cook according to package directions. Drain and set aside.
In a large skillet, melt 2 tablespoons of butter. Add the shrimp, salt, pepper and garlic powder. Stir several times until shrimp is cooked (about 5 minutes). Remove from heat.
In a medium saucepan over a medium high heat, pour in the marinara sauce and heavy cream. Stir constantly until heated through. Stir in the parmesan cheese. The sauce should thicken as it heats and as you stir.
Place the penne pasta in a large bowl. Pour the creamy marinara sauce over the pasta and add the shrimp to the bowl. Stir well until everything is mixed throughout.
Serve and garnish with fresh, torn basil leaves and freshly grated parmesan cheese, if you'd like.