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 together and simmer on low heat for 3 minutes. Pour the filling evenly into the prepared baking dish.
06 - In a large mixing bowl, whisk together the flour, baking powder, garlic powder, sugar, and salt. Cut in the cold cubed butter using a pastry blender or fork until the mixture resembles coarse crumbs.
07 - Fold in the shredded cheddar cheese and chopped parsley. Pour in the milk and mix gently just until combined, being careful not to overwork the dough.
08 - Drop spoonfuls of the biscuit dough evenly over the chicken filling, covering the surface as uniformly as possible.
09 - Bake for 25 to 30 minutes, or until the biscuit topping is golden brown and cooked through.
10 - While the cobbler bakes, combine the melted butter, garlic powder, and chopped parsley in a small bowl.
11 - Remove the cobbler from the oven and immediately brush the tops of the biscuits generously with the garlic parsley butter. Allow to cool for 5 minutes before serving.