How to Make It
Heat a slow cooker on high until hot. Stir in 2 tablespoons of the butter until melted, then stir in the bread cubes. Cook the bread cubes, stirring, until browned and crisp, about 5 minutes. Transfer the bread cubes to a bowl and reserve.
Stir in the remaining 1 tablespoon butter until melted, then stir in the chicken, 3/4 teaspoon salt and 1/2 teaspoon pepper, and cook until golden, about 8 minutes. Sprinkle the flour over the chicken, stirring to combine. Stir in the onions, celery, and stock, then reduce the heat to low. Cook the soup until the chicken is very tender, 6 to 8 hours.
Remove the chicken and let cool to warm. Remove the meat, discarding the bones. Return the chicken to the slow cooker. Stir in the cream and season with salt and pepper to taste. Serve the soup topped with the reserved breadcrumbs.