01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with butter or nonstick spray.
02 - In a large skillet over medium heat, melt 2 tablespoons of butter. Add the diced onion and cook until translucent, about 3 minutes. Stir in the minced garlic and cook for 1 additional minute until fragrant.
03 - Sprinkle 3 tablespoons of flour over the onion and garlic. Cook, stirring constantly, for 1 minute to form a roux and remove the raw flour taste.
04 - Slowly whisk in the chicken broth, followed by the whole milk. Continue stirring and cooking until the sauce thickens, about 2 to 3 minutes.
05 - Add the shredded chicken, thawed peas and carrots, corn, dried thyme, sea salt, and black pepper. Stir everything to combine and simmer on low heat for 3 minutes. Pour the filling into the prepared baking dish.
06 - In a large bowl, whisk together the flour, baking powder, garlic powder, sugar, and salt until evenly distributed.
07 - Add the cold cubed butter to the flour mixture. Using a pastry blender or fork, cut the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
08 - Stir in the shredded cheddar cheese and chopped parsley. Pour in the milk and mix just until combined — be careful not to overmix or the biscuits will become tough.
09 - Drop spoonfuls of the biscuit dough evenly over the chicken filling, covering as much of the surface as possible.
10 - Bake for 25 to 30 minutes, or until the biscuit topping is golden brown and cooked through.
11 - While the cobbler bakes, combine the melted butter, garlic powder, and chopped parsley in a small bowl.
12 - Remove the cobbler from the oven and immediately brush the tops of the biscuits generously with the garlic butter. Let cool for 5 minutes before serving.