Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking dish.
In a large skillet over medium heat, melt 1 tablespoon of butter. Add onion and garlic; cook and stir until onion is tender. Stir in flour, bouillon, and pepper. Gradually stir in milk and sour cream. Cook and stir until thickened. Remove from heat and stir in thyme and oregano.
In the prepared baking dish, layer chicken, tomatoes, mushrooms, and cheese. Pour sauce over all. In a small bowl, combine melted butter and bread crumbs; sprinkle over top.
Bake in preheated oven for 30 minutes, or until bubbly.
Interesting Facts
The word casserole comes from the French word “cassa” meaning “pan”.
Casseroles have been around since the 1700’s.
Casseroles are popular dishes in many countries around the world.