Preheat the oven to 350 degrees. Add the stick of butter to a 9x13" baking dish, and place it in the preheating oven just until melted. Spread the chicken evenly out over the bottom of the dish. Salt & pepper the chicken layer, to taste.
Do NOT MIX the layers, and follow the steps exactly. In a small mixing bowl, whisk together the bisquick, half & half, and thyme until evenly combined. Slowly pour the mixture evenly out over the chicken, so as not to move the chicken around.
In another mixing bowl, whisk together the broth, soup, poultry seasoning, garlic, & onion powder until evenly combined. Again, slowly pour this mixture evenly out over the bisquick layer- again careful not to disturb it too much.
Bake the casserole at 350 degrees for 50-60 minutes, or until the casserole is set and the top has formed a gorgeous golden browned crust.