Prepare Shells
Cook shells per instructions, salting water. Drain.
Prepare Filling
Cook shallot and bell peppers in olive oil until tender, 4-5 minutes. Cool.
Combine cooked vegetables, mozzarella, parmesan, mayo, milk, egg, panko, crab meat, shrimp, seafood seasoning, salt, and pepper.
Stuff Shells
Stuff each shell with 1 tbsp filling.
Prepare Sauce
Melt butter. Cook onion until tender, 4-5 minutes.
Add garlic, salt, and pepper. Cook 1 minute.
Whisk in flour until absorbed, 3-4 minutes.
Slowly whisk in heavy cream and milk until incorporated, 2-3 minutes.
Stir in seafood seasoning, salt, and pepper. Cook 10-15 minutes until thickened.
Stir in fontina cheese until melted.
Bake and Serve
Place stuffed shells in a baking dish.
Pour sauce over shells, reserving 1 cup.
Bake at 350°F (175°C) for 25-30 minutes.
Garnish with parsley. Serve with reserved sauce.
