Slow Cooker Pennsylvania Dutch Chicken Pot Pie

Heat a slow cooker on high until hot. Stir in the butter until melted, then stir in the onions, celery, 3/4 teaspoon salt and 1/2 teaspoon pepper and cook, stirring occasionally, until golden, 6 to 8 minutes. Stir in the flour and cook 2 minutes. Stir in the stock, chicken, noodles and thyme, then reduce the heat to low. Cook until the chicken is very tender and the noodles are falling apart, 6 to 8 hours. Season the pot pie with salt and pepper to taste, then serve.