Begin by cutting the gluten-free bread into ½-inch cubes. Spread the cubes out on baking sheets to dry at room temperature for 24 hours or toast in the oven at 225°F for 30-40 minutes.

While the bread is drying, grease a 9x13-inch baking dish with ½ tablespoon of butter. Preheat your oven to 350°F.

In a large skillet, melt 6 tablespoons of butter over medium heat. Add the diced celery and onion, sautéing for 8-10 minutes until soft and translucent.

Stir in the minced parsley, dried sage, thyme, marjoram, salt, and pepper, cooking for an additional minute. Remove from heat and allow to cool slightly.

In a large mixing bowl, whisk together the eggs and egg yolk. Add the dried bread cubes, diced apple, sautéed vegetables, and chicken broth. Gently stir to combine.

Pour the stuffing mixture into the prepared baking dish, spreading it evenly. Drizzle any remaining melted butter over the top and cover with aluminum foil.

Bake the covered dish in the preheated oven for 25 minutes to steam the stuffing.

Remove the foil and return to the oven for an additional 20-25 minutes until the top is golden brown and crispy.