Grease a pie plate or baking dish generously with butter or cooking spray. In a large bowl, mix the pumpkin puree, pumpkin spice mix, milk and egg. Add the corn muffin mix and whisk together until combined.
Pour batter into the pie plate or baking dish and let sit for 3 minutes while making the walnut topping. In a small bowl, combine the walnuts and brown sugar. Toss until the walnuts are coated with the brown sugar.
Oven Baking: Sprinkle the topping over the cornbread batter. Bake for 20 to 25 minutes in an oven preheated to 400℉.
Air Frying: If cooking in your air fryer, set the temperature to 350℉ and the time to 10 minutes. Place the baking dish in the air fryer, adding the walnut topping during the last 5 minutes. Check the cornbread with a toothpick when the 10 minutes is up, and continue to cook in 2 minute increments if it's not fully cooked.
Let cool 5 minutes before serving.
Notes
Storing: pumpkin cornbread should be covered and stored at room temperature for up to 5 days. It can be frozen for up to 6 months when stored in freezer safe storage containers.