Preheat the oven to 425 degrees F. Put the chicken in a 2-quart casserole dish. Combine the broth and soup in a medium saucepan and bring the mixture to a boil. Pour the broth mixture over the chicken. In a separate medium bowl, mix the flour with the pepper. Stir in the melted butter and the buttermilk. Pour this mixture over the casserole and smooth the top; do not stir. Bake the casserole until the crust is brown and the filling beneath is hot and bubbly, 45 minutes.