Prepare the Seafood: Clean and devein the shrimp if necessary, removing shells and tails. In a skillet, melt 1 tablespoon of butter over medium heat. Add minced garlic and sauté for about a minute until fragrant. Add the mixed seafood and cook for 3-4 minutes until just cooked through. Be careful not to overcook as it will continue cooking in the oven. Remove seafood from the skillet and set aside.

Cook the Pasta: Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package instructions until al dente. Drain the pasta and set aside.

Make the Cheese Sauce: In the same pot used for pasta, melt the remaining tablespoon of butter over medium heat. Add flour and whisk constantly for 1-2 minutes until the mixture turns slightly golden. Gradually pour in milk while whisking continuously to prevent lumps. Cook for about 5 minutes until the mixture thickens.

Add Cheeses: Reduce heat to low and add the shredded cheddar, Gruyere, and Parmesan cheeses. Stir until the cheeses melt completely and the sauce becomes smooth and creamy. Season with paprika, cayenne pepper, salt, and pepper to taste.

Combine Ingredients: Preheat oven to 350°F (175°C). In a large mixing bowl, combine the cooked seafood, pasta, and cheese sauce. Gently fold everything together until well coated with the cheese sauce.

Bake to Perfection: Transfer the mixture to a greased baking dish, spreading it evenly. Bake in the preheated oven for 20-25 minutes until the top turns golden brown and the edges are bubbling.

Serve: Remove from oven and let cool for a few minutes to allow flavors to meld. Garnish with freshly chopped parsley before serving.