Preheat oven to 350 degrees F.

In a small mixing bowl mix lump crab meat with grated Parmesan, Old Bay, garlic and Ricotta; set aside.

Cook jumbo shells according to package directions and drain; shake gently to make sure they're dry.

Heat butter in a small skillet, add dry white wine and marjoram with shrimp and cook until wine dissipates; set aside to cool.

Once cool, stir shrimp into the crab and Ricotta mixture.

Heat butter in a large skillet with garlic, add dry white wine and cook a couple of minutes.

Stir in flour and add the cold milk all at once.

Stir and as it thickens remove from heat, and stir in the heavy cream, Parmesan and nutmeg.

Spoon some of the sauce into the bottom of an oblong casserole, just enough to cover. Set the rest of the sauce aside.

Fill shells with mixture placing filling side up in the baking dish. Continue until filling is used up.

Add ¼ cup water to remaining sauce, since it is likely thickened and spoon over the shells in the casserole.

Cover the sauced shells with shredded cheese.

Bake uncovered for 25-35 minutes or until lightly browned and bubbly.

Garnish with crushed seasoned croutons if desired.