Start by taking your cooked shrimp and giving them a nice chop if they are too large. You want them bite-sized, so they mix well with the pasta.
Melt the cubes of butter in a spacious saucepan over medium heat. Once it is bubbling and smells buttery, toss in the minced garlic. Watch it closely to avoid burning.
Pour in the heavy whipping cream, stirring gently as it bubbles. The cream will swirl together with the butter and garlic, becoming luscious and velvety.
Add the garlic powder, Italian seasoning, salt, and pepper into the creamy mixture. Stir it in well.
Take your cooked penne and pour it into the sauce. Stir it all together until every piece of pasta is coated nicely.
Mix in the shredded mozzarella and half of the grated Parmesan. Let it melt and blend for that creamy finish.
Gently fold the chopped shrimp into the pasta mix, ensuring they are evenly distributed.
Spoon the entire mixture into a greased baking dish, smoothing it out.
Sprinkle the remaining Parmesan cheese over the top evenly.
Pop the dish into the oven and bake until bubbly and golden on top.