Preheat oven to 400°F (200°C).

In a large skillet over medium heat, melt the butter. Add the onion, celery, and bell pepper and cook until softened, about 5-7 minutes. Stir in the garlic and cook for 1 more minute.

Sprinkle the flour over the vegetables and stir constantly for 2 minutes to cook out the raw flour taste.

Slowly whisk in the seafood stock until smooth. Bring to a simmer, then stir in the heavy cream and Creole seasoning. Let the sauce thicken for a couple of minutes.

Reduce heat to low. Gently stir in the shrimp, fish, and frozen corn. Cook for 2-3 minutes, just until the shrimp begin to turn pink. Remove from heat and stir in the parsley and lemon juice. Season with salt and pepper to taste.

Pour the filling into a 9-inch pie plate or similar-sized casserole dish.

Lay the puff pastry over the filling. Trim and crimp the edges if desired. Brush the top with the egg wash and cut a few slits in the center for steam to escape.

Place on a baking sheet and bake for 20-25 minutes, or until the pastry is puffed and golden brown and the filling is bubbly.

Let the pot pie rest for at least 10 minutes before serving.