Isabelle's Seafood Casserole

1 . Stage

Melt 3 tablespoons butter in a large Dutch oven over medium heat; stir in celery and onion. Cook and stir until translucent, 5 to 7 minutes. Season with salt and pepper and remove to a bowl. Leave grease in the Dutch oven.

2 . Stage

At the same time, melt 1 tablespoon butter in a skillet over medium-high heat. Add scallops to the hot skillet in a single layer without crowding. Cook until golden brown and sizzling and opaque all the way through, about 2 minutes per side. Remove from heat.

3 . Stage

Add flour to the Dutch oven; whisk over medium-low heat until mixture becomes paste-like and light golden brown, about 5 minutes. Gradually whisk milk into the flour mixture, and bring to a gentle boil. Add Cheddar cheese and remaining 1/2 cup butter. Incorporate celery-onion mixture and simmer until thickened, 5 to 10 minutes.

4 . Stage

While the mixture is simmering, set an oven rack about 6 inches from the heat source and preheat the oven's broiler.

5 . Stage

Stir scallops, shrimp, lobster, and crabmeat into the Dutch oven, then pour into a 9x13-inch baking dish.

6 . Stage

Broil in the preheated oven until browned on top, 2 to 3 minutes.