Preheat the oven to 400°F. Grease a 9x13-inch baking dish with cooking spray.

Prepare the filling: Heat the oil in a large skillet over medium heat. Add the onion and sauté until translucent and softened, about 4 minutes. Add the garlic and thyme, and cook, stirring constantly, until fragrant, about 1 minute. Add the butter, stirring constantly to melt. Add the flour and cook, stirring constantly, until it has adhered to the mixture and no clumps remain, about 2 minutes.

Make the gravy and add the vegetables and chicken: Gradually add the broth, about 1 cup at a time, whisking constantly until thickened and smooth, about 4 minutes. Whisk in the heavy cream, salt, and pepper until incorporated. Stir in the mixed vegetables and chicken. Remove from the heat. Transfer to the prepared baking dish. Set aside.

Prepare the biscuit topping: Whisk together the flour, baking powder, sugar, garlic powder, baking soda, and salt in a medium bowl until combined. Toss in the cold butter pieces and cut in with a pastry cutter or fork until crumbly and the butter pieces are pea-sized. Stir in the buttermilk and cheddar cheese until no pockets of dry flour remain, using your hands if needed.

Form the biscuit top: Drop 12 (¼-cupfuls) of dough evenly on top of the chicken mixture in the baking dish.

Bake: Bake until the biscuits are golden brown, a toothpick inserted in biscuit centers comes out clean, and the cobbler is bubbly, 25 to 30 minutes. Rotate the pan from front to back halfway through the bake time. Remove from the oven and let cool for about 5 minutes.

Add the butter topping: While cobbler bakes, stir together the melted butter, Old Bay seasoning, and garlic powder. Brush the warm biscuit topping with the butter mixture and serve hot. Store leftovers in an airtight container for up to 3 days. Love the recipe? Leave us stars and a review below!