Preheat the oven to 350°F (175°C). Spread the cubed rye bread evenly on a large baking sheet. Bake for 10 minutes, or until lightly dried. Remove from the oven and set aside.
Cook the vegetables:
In a large skillet, melt 3 tablespoons of butter over medium heat. Add the onion, apple, and celery. Cook for 8–10 minutes, stirring occasionally, until softened. Season with salt and pepper. Add the garlic, thyme, sage, and parsley, and cook for 1 additional minute until fragrant.
Combine ingredients:
Place the toasted bread cubes into a large mixing bowl. Add the cooked vegetable mixture, the beaten egg, and vegetable broth. Stir gently to combine, ensuring the bread is evenly moistened. Allow the mixture to rest for 5 minutes.
Bake the stuffing:
Transfer the mixture to a greased 9x13-inch baking dish. Bake for 40 minutes, stirring every 10 minutes for even texture. For the final 10 minutes, melt the remaining 1 tablespoon of butter and drizzle it over the top. Continue baking until the stuffing is golden brown on top.
Notes
To prepare this recipe gluten free, substitute the marbled rye bread with a certified gluten-free rye-style or multigrain bread. Additionally, ensure the vegetable broth and all dried herbs are certified gluten free to avoid cross-contamination.