Oyster and Rockfish Pot Pie

Name: Oyster and Rockfish Pot Pie
Ingredients: 3 tablespoons olive oil; 1 tablespoon unsalted butter; 1/2 cup button mushrooms, quartered; 1/2 cup medium-diced potatoes; 1/4 cup medium-diced carrots; 1/4 cup medium-diced leeks; 3 stalks celery, medium diced; 2 cloves garlic, finely chopped; 1 small onion, medium diced; 1/4 cup all-purpose flour; 1 cup white wine; 3 cups fish stock; 1 cup heavy cream; 1 pound rockfish, skinned and cut into 1-inch cubes; 2 dozen oysters, shucked; 1 tablespoon chopped fresh chives; 1 tablespoon chopped fresh parsley; 1 tablespoon chopped fresh thyme; 1 lemon, juiced; Salt and freshly ground black pepper; 6 large puff pastry rounds, chilled (1/8-inch thick and 4 inches round); 1 egg, beaten