Preheat the oven to 375°F and lightly grease a 9x13-inch baking dish.
In a large bowl, combine the shredded chicken, cream of chicken soup, chicken broth, mixed vegetables, and 1 cup shredded cheddar cheese. Stir until evenly combined.
Transfer the filling to the prepared baking dish and spread evenly.
Prepare the Cheddar Bay biscuit mix according to package directions. Stir in the additional cheddar cheese if desired.
Drop spoonfuls of biscuit dough evenly across the filling, leaving small gaps between portions.
Bake for 25 to 30 minutes until the filling is bubbling around the edges, the cheese is melted, and the biscuits are golden brown.
Mix the melted butter with the garlic butter seasoning packet and brush over the hot biscuits immediately after baking.
Allow the casserole to rest for 10 minutes before serving.
Notes
Use rotisserie chicken for convenience and extra flavor. The filling should be creamy but not overly soupy to ensure the biscuits bake properly. Allow the casserole to rest for 10 minutes before serving. Brush the garlic butter seasoning over the biscuits immediately after baking for maximum flavor. Refrigerate leftovers for up to 4 days or freeze for up to 3 months.