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 butter. Add diced onion and cook until translucent, about 3 minutes. Stir in minced garlic and cook 1 minute more until fragrant.
03 - Sprinkle 3 tablespoons flour over the onion and garlic. Cook, stirring constantly, for 1 minute to form a smooth roux.
04 - Slowly whisk in 1½ cups chicken broth, followed by ½ cup whole milk. Stir and cook until the sauce thickens, about 2 to 3 minutes.
05 - Add shredded chicken, peas and carrots, corn, dried thyme, sea salt, and black pepper. Stir to combine and simmer on low for 3 minutes. Pour the filling into the prepared baking dish.
06 - In a large bowl, whisk together 1½ cups flour, baking powder, garlic powder, sugar, and salt.
07 - Cut in 1/3 cup cold cubed butter using a pastry blender or fork until the mixture resembles coarse crumbs.
08 - Stir in shredded cheddar cheese and 2 tablespoons parsley. Pour in ¾ cup milk and mix just until combined. Do not overmix.
09 - Drop spoonfuls of the biscuit dough evenly over the chicken filling to cover the surface.
10 - Bake for 25 to 30 minutes or until the biscuit topping is golden brown and cooked through.
11 - While baking, combine 2 tablespoons melted butter, ½ teaspoon garlic powder, and 1 tablespoon chopped parsley in a small bowl.
12 - Remove cobbler from oven and immediately brush the tops of the biscuits with the garlic parsley butter. Let cool 5 minutes before serving.