Preheat oven to 400°F (200°C).

Make the Filling: In a large oven-safe skillet, melt 4 tbsp of butter over medium heat. Add onion, carrots, and celery and cook until softened, about 5-7 minutes. Stir in the minced garlic and cook for 1 minute more until fragrant.

Create the Sauce: Sprinkle the flour over the vegetables and stir for 2 minutes. Gradually whisk in the stock and heavy cream until smooth. Bring to a simmer and cook until thickened, about 3-4 minutes.

Add Seafood: Remove from heat. Stir in the Old Bay seasoning, dried parsley, salt, and pepper. Gently fold in the shrimp, crab meat, peas, and corn. Set aside.

Make the Biscuit Topping: In a bowl, whisk together flour, baking powder, sugar, salt, and 1/2 tsp garlic powder. Cut in the cold butter until the mixture resembles coarse crumbs. Stir in the cheddar cheese.

Form Dough: Pour in the cold buttermilk and mix just until a shaggy dough forms. Do not overmix.

Assemble and Bake: Drop large spoonfuls of biscuit dough over the seafood filling. Bake for 20-25 minutes, or until the filling is bubbly and biscuits are golden brown.

Finish with Garlic Butter: While baking, mix the melted butter, 1/4 tsp garlic powder, and fresh parsley. As soon as the pot pie comes out of the oven, brush the hot biscuits with the garlic butter. Let rest for a few minutes before serving.