📋 Instructions

1. 1Heat the Oven and Prep — Preheat the oven to 400F (200C). Lightly grease a 9x13-inch baking dish and set it aside. Have all your ingredients measured and ready, because the filling comes together quickly.
2. 2Cook the Vegetables — Melt the butter in a large skillet over medium heat, about 2 minutes, until it foams. Add the thawed mixed vegetables and cook for 4 minutes, stirring, until they are hot and glossy.
3. 3Make the Roux — Sprinkle the flour over the vegetables and stir constantly for 1 to 2 minutes, until the flour smells toasty and no dry streaks remain. This step removes the raw flour taste.
4. 4Build the Creamy Sauce — Pour in the 2 1/2 cups milk in a steady stream, whisking constantly. Add the poultry seasoning, salt, and pepper. Cook for 4 to 5 minutes, whisking, until the sauce thickens enough to coat the back of a spoon and bubbles gently at the edges.
5. 5Add the Chicken — Stir in the cooked chicken and cook for 2 minutes more, just until heated through. Taste and adjust the salt. Pour the filling into the prepared baking dish and spread it evenly.
6. 6Mix the Biscuit Topping — In a medium bowl, stir the biscuit baking mix and 1/2 cup milk together just until a soft, shaggy dough forms, about 20 seconds. Do not overmix.
7. 7Drop and Top — Drop the dough by rounded spoonfuls over the filling, spacing them evenly; they will spread as they bake. Scatter the Parmesan or cheddar over the top if using.
8. 8Bake Until Golden — Bake at 400F (200C) for 25 to 30 minutes, until the biscuits are deep golden brown and the filling bubbles at the edges. A knife inserted into the center should come out hot. Let it rest for 10 minutes before serving.