Boil a large pot of salted water and cook large pasta shells for about 9–10 minutes, stopping 1–2 minutes before al dente. Drain and rinse under cold water.

In a large mixing bowl, combine cooked seafood with softened cream cheese and minced garlic and mix until smooth.

In a medium saucepan, melt butter over medium heat and stir in flour to make a roux. Gradually add milk while whisking, cooking until the sauce thickens, about 5–7 minutes.

Preheat oven to 375°F (190°C). Fill each cooled pasta shell with the creamy seafood mixture, place in a greased baking dish, and pour sauce evenly over the shells. Sprinkle with shredded cheese.

Cover with aluminum foil and bake for 25–30 minutes. Remove foil in the last 15 minutes to brown the cheese.