Grease a 9-inch deep-dish pie plate (or an 8-inch or 9-inch square baking dish). Preheat oven to 425°F.
In a large bowl, stir together the condensed soup, milk, chicken, thawed broccoli, cheese, and thyme. Taste and season with salt and black pepper, if necessary.
Transfer the chicken mixture to the prepared dish. Cover with foil and bake for about 10 minutes while you prepare the biscuit topping.
PREPARE THE BISCUITS
Use a fork to stir together the Bisquick mix, buttermilk, cheese, and parsley until a soft dough forms. Start with ½ cup of buttermilk, and gradually add more (if needed) to bring the dough together. It shouldn't be too wet, but you don't want any dry pockets of flour.
Drop mini biscuits by rounded tablespoonful on top of the hot chicken mixture.
Return the dish to the oven and bake, uncovered, for about 17-20 minutes, or until the biscuits are golden brown and a toothpick inserted in a biscuit comes out clean. If the biscuits start to get too dark on top before they're cooked through, just tent loosely with aluminum foil and continue baking.
Stir together melted butter and garlic powder; brush over warm biscuits and serve.
Use a cookie dough scoop or a heaping tablespoon to scoop mini biscuits onto the filling. These smaller biscuits cook through faster than larger biscuits.
Make sure that the biscuits are cooked all of the way through before pulling the casserole out of the oven. They should be golden brown on the outside and a toothpick inserted in the center should come out clean.
If the biscuits start to get too dark before they’re completely cooked through, tent the dish with foil and continue baking.
Garnish the finished pot pie with fresh dill or other herbs for even more flavor.