Dice bacon and sauté in melted butter. Remove crispy bacon and add onion, celery, carrot, and leek. Season with salt and pepper and cook until softened. Add two-ish tablespoons of flour and for a few minutes. Deglaze with white wine, add a splash of chicken stock, and the meat from a rotisserie chicken. Add 3/4 of a container of crème fraiche and cooked bacon, stir until combined. Pour into a cast iron skillet, cover with puff pastry, and bake at 350 degrees for about 20 minutes.