Make the Biscuit Topping: In a large bowl, whisk together the flour, baking powder, and salt. Add the cold, cubed butter and cut it into the dry ingredients using a pastry cutter or pulse in a food processor until coarse crumbs form. Stir in 1 cup of milk until the dough comes together. Shape the dough into 8 or 9 discs, place on a lined plate, cover, and refrigerate.
Prepare the Filling: Melt butter in a large skillet over medium heat. Add onion, carrots, celery, mushrooms, and garlic. Cook for 5 minutes until softened. Stir in flour, salt, pepper, and thyme until the flour absorbs the liquid. Add broth and milk, simmer for 7-9 minutes until thickened. Stir in mixed vegetables and parsley, then remove from heat.
Assemble the Pot Pie: Preheat the oven to 400F (204C). Pour the filling into a greased 2.5- or 3-quart baking dish. Arrange the chilled biscuits on top, squeezing them in as needed. Brush the tops with the remaining 2 Tablespoons of milk.
Bake: Bake for 25 minutes, then increase the oven temperature to 425F (218C) and bake for 5-6 more minutes, or until the biscuits are golden brown. Let cool for 5 minutes before serving.
Notes
Keep butter cold for flaky biscuits: Cold butter creates steam pockets during baking, resulting in that perfect flaky texture.
Do not overmix the biscuit dough: Mix just until the dough comes together to avoid tough biscuits.
Thicken the filling properly: Simmer the sauce for the full 7-9 minutes to ensure it thickens enough to coat the vegetables.
Make ahead option: Prepare the filling and biscuits separately, then assemble and bake when ready to serve.
Freezing instructions: Assemble the pot pie, cover tightly, and freeze for up to 3 months. Bake from frozen, adding extra time as needed.
Variations: Add cooked chicken, turkey, or tofu for protein, or swap vegetables based on what is in season.
