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 roux and cook out the raw flour taste.
04 - Slowly whisk in 1½ cups chicken broth, followed by ½ cup whole milk. Continue stirring and cooking until the sauce thickens, about 2-3 minutes.
05 - Add shredded chicken, thawed 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 until evenly distributed.
07 - Cut the cold cubed butter into the flour mixture using a pastry blender or fork until it resembles coarse crumbs with pea-sized pieces.
08 - Stir in shredded cheddar cheese and chopped parsley. Pour in ¾ cup milk and mix just until combined — do not overmix or the biscuits will be tough.
09 - Drop spoonfuls of biscuit dough evenly over the chicken filling, covering as much surface area as possible.
10 - Bake for 25-30 minutes until the biscuit topping is golden brown and cooked through.
11 - While the cobbler bakes, combine melted butter, garlic powder, and chopped parsley in a small bowl.
12 - Remove cobbler from the oven and immediately brush the tops of the biscuits generously with the garlic butter. Let cool for 5 minutes before serving.