01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish or large ovenproof skillet.
02 - In a large skillet over medium heat, melt 4 tablespoons butter. Add onion, carrots, and celery; sauté until softened, about 5 minutes.
03 - Sprinkle in 1/4 cup flour; stir and cook for 2 minutes.
04 - Gradually whisk in seafood stock and milk (and wine, if using), stirring constantly until smooth. Bring to a simmer and cook until thickened, 5–7 minutes.
05 - Stir in Old Bay, salt, pepper, and parsley. Add shrimp, crab, fish, and peas. Cook gently for 2–3 minutes.
06 - Pour the seafood mixture into the prepared baking dish.
07 - For the biscuit topping, whisk together flour, baking powder, baking soda, garlic powder, sugar, and salt in a large bowl.
08 - Cut in cold butter with a pastry cutter or fingers until mixture resembles coarse crumbs. Fold in cheddar and herbs.
09 - Stir in cold buttermilk just until dough comes together.
10 - Drop large spoonfuls of biscuit dough evenly over the seafood filling.
11 - Bake 25–30 minutes, until biscuit topping is golden and cooked through.
12 - While baking, mix melted butter, garlic powder, and parsley for the glaze.
13 - As soon as the pot pie comes out of the oven, brush biscuits with the garlic butter glaze.
14 - Let cool 10 minutes before serving.