Begin by cooking the large pasta shells in a large pot of salted boiling water for about 9 minutes, just until al dente. Drain and rinse them under cool water to stop the cooking process, preventing them from becoming too soft. Arrange the shells on a clean kitchen towel, ensuring they do not stick together.

In a skillet over medium heat, melt a tablespoon of butter and sauté minced garlic for about 1 minute, just until fragrant. Add the prawns and crab meat, cooking until the prawns turn pink and opaque, roughly 5-6 minutes. Remove from heat and stir in cream cheese, mixing until smooth and creamy. Adjust seasoning to taste, then set the filling aside.

In a medium saucepan, melt 3 tablespoons of butter over low heat. Sprinkle in 3 tablespoons of flour, whisking constantly for about 2 minutes to form a roux. Gradually pour in 2 cups of milk, whisking until the mixture is smooth and starts to thicken, roughly 5 minutes. Stir in the cheddar cheese until melted and combined.

Preheat your oven to 180°C (160°C Fan). Spoon a portion of the creamy cheese sauce into the bottom of a greased baking dish. Carefully fill each pasta shell with the seafood mixture using a spoon, placing them in the dish seam-side up. Pour the remaining cheese sauce over the top.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25-30 minutes, until bubbly and heated through. Remove the foil during the last 10 minutes to allow the top to become beautifully golden.

Once baked, remove the dish from the oven and let it cool for about 5 minutes. Dish out the creamy seafood stuffed shells, garnishing with freshly chopped parsley.