Chicken Pot Pie Casserole

Preheat the oven to 375 degrees Fahrenheit. Set a large dutch oven or heavy bottom skillet over medium heat and add in butter. Once the butter has melted, add diced onion and cook until translucent, about 3-5 minutes. Add thyme, garlic, flour, salt, and cracked pepper and stir until pasty, about 1-2