For the gluten-free bread cubes:

1. Preheat the oven to 300F. With a knife, cube 10 slices of bread into small, even, cubed-shaped pieces.
2. Spread the bread cubes in an even layer onto the baking sheet.
3. Bake for 10 minutes or until lightly golden, stirring if needed. Remove from the oven and set aside.

For the stuffing:

1. Meanwhile, in a large skillet, cook the sausage over medium-high heat, breaking up the meat with a spatula as it browns. Remove the sausage from the skillet with a slotted spoon and transfer it to a plate. Keep the drippings in the pan.
2. To the same skillet, add the leeks, apples, celery, and poultry seasoning. Cook for 10 minutes until the leeks are softened and golden brown. 
3. Stir in the cranberries, cooked sausage, and bread cubes. Season with salt and black pepper, and toss to combine before adding the chicken broth. The stuffing is supposed to appear wet and soggy, but as it bakes, the moisture will evaporate, and the mixture will become more cohesive. 
4. Preheat oven to 350F and grease a 9×13-inch baking dish.
5. Transfer the stuffing inside the pan and cover it with foil. Bake, covered for 45 minutes. Remove the foil and bake for an additional 12 to 15 minutes until the top is golden. Remove from oven and keep warm or serve.

To use as stuffing in a turkey:

1. Place 4 to 6 cups of the stuffing mixture inside a 12 to 16 lb turkey, about 1 cup for every 2 to 3 lbs. Tie the legs and bake until the turkey thigh reaches an internal temperature of 175F and the breast and stuffing reach 165F. 
2. Any leftover stuffing can be baked in a separate casserole dish as a side serving.