Step 1: In a large skillet or Dutch oven, melt 2 tablespoons of butter over medium heat. Add the diced onion and celery and cook until softened, about 5-7 minutes. Add the minced garlic and cook for another minute until fragrant.
Step 2: Stir in the remaining 2 tablespoons of butter until melted. Gradually whisk in ¼ cup all-purpose flour, cooking for 1-2 minutes to create a roux.
Step 3: Slowly pour in the milk and broth, whisking constantly to prevent lumps. Bring the mixture to a simmer, then reduce heat and cook, stirring, until the sauce thickens, about 5-7 minutes.
Step 4: Remove from heat and stir in ½ cup shredded cheddar cheese, Old Bay seasoning, salt, and pepper until the cheese is melted and the sauce is smooth. Gently fold in the crab meat, chopped shrimp, and flaked white fish. Pour the seafood mixture into a 9x13 inch baking dish.
Step 5: Prepare the Biscuit Topping: In a large bowl, whisk together 2 cups flour, baking powder, and ½ tsp salt. Cut in the cold, cubed butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Stir in ¾ cup shredded cheddar cheese.
Step 6: Gradually add ⅔ cup milk, mixing just until a soft dough forms. Do not overmix. Drop spoonfuls of biscuit dough over the seafood filling in the baking dish, leaving small gaps.
Step 7: Preheat your oven to 375°F (190°C). Bake the pie for 25-30 minutes, or until the biscuit topping is golden brown and the filling is bubbly. During the last 5 minutes, prepare the garlic butter by melting 2 tablespoons of butter and stirring in 1 minced garlic clove and 1 tbsp chopped parsley.
Step 8: Once the pie is out of the oven, brush the warm biscuit topping generously with the garlic butter mixture. Let the pie rest for 5-10 minutes before serving. Enjoy your delicious Cheddar Bay Seafood Pie!
Step 9: For more detailed information on different types of crab meat, you can visit a culinary resource like CulinarySchools.org.