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 for 1 additional minute until fragrant.
03 - Sprinkle 3 tablespoons flour over the onion and garlic mixture. Cook, stirring constantly, for 1 minute to form a smooth roux.
04 - Slowly whisk in chicken broth, followed by milk. Continue stirring and cooking 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 heat for 3 minutes. Pour the filling into the prepared baking dish.
06 - In a large bowl, whisk together flour, baking powder, garlic powder, sugar, and salt until evenly combined.
07 - Cut the cold cubed butter into the dry mixture using a pastry blender or fork until it resembles coarse crumbs with pea-sized pieces.
08 - Fold in shredded cheddar cheese and chopped parsley. Pour in milk and mix just until combined, being careful not to overwork the dough.
09 - Drop generous spoonfuls of the biscuit dough evenly across the surface of the chicken filling to create a rustic, cobbled topping.
10 - Bake for 25 to 30 minutes until the biscuit topping is golden brown and cooked through.
11 - While baking, 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 glaze. Let cool for 5 minutes before serving.