Preheat oven to 350F.

Cook pasta shells in boiling water according to package directions.

Drain, rinse, and cool the cooked pasta shells.

Melt 1 tablespoon of butter in a skillet over medium heat.

Add chopped green peppers and red onion to the skillet.

Cook the vegetables until softened, about 3-5 minutes.

In a bowl, combine lump crabmeat, sautéed peppers and onions, black pepper, beaten egg, mayonnaise, 1/2 teaspoon Old Bay seasoning, and 1/2 cup of milk.

Melt 1/2 teaspoon of butter in each of two 11"x7"x2" baking dishes.

Spoon the crab mixture into the cooked pasta shells.

Arrange the filled shells in the prepared baking dishes.

Melt the remaining butter in a saucepan over medium-low heat.

Whisk in all-purpose flour and cook for 1 minute to form a roux.

Gradually whisk in the remaining milk, stirring constantly to prevent lumps.

Cook the sauce until it slightly thickens.

Stir in the grated Parmesan cheese until melted and smooth.

Drizzle the cheese sauce evenly over the filled pasta shells in the baking dishes.

Sprinkle the remaining Old Bay seasoning over the sauced shells.

Bake in the preheated oven for 30 minutes, or until bubbly and golden brown.

Remove from the oven and let cool for 10 minutes before serving.