1 package of 8 potato bread hamburger buns, about 1 pound
2 stalks celery, diced into 1/4-inch cubes
1 1/2 sticks unsalted butter
1/4 cup chopped fresh sage 1 large onion, diced into 1/4-inch cubes
2 cups turkey or chicken broth, slightly warmed
1/2 pound mild Italian turkey sausage (about 4 links, casing removed)
1 teaspoon kosher salt
2 cups sliced mushrooms
1/2 teaspoon black pepper
Preheat the oven to 375 degrees Fahrenheit
Tear the hamburger buns into 1-inch pieces. Place on a baking sheet and bake for about 10 minutes, turning once, until crisp and slightly toasted. Remove from the oven and allow to cool. (You can make this a day ahead.)
In a very large skillet, melt the butter over medium heat. Add the onions, sausage, mushrooms and celery. Cook slowly for about 12 to 15 minutes until the onions soften.
Stir in the toasted bread cubes. Add the warm broth, salt and pepper; stir until combined. Adjust seasoning with additional salt and pepper if desired.
Transfer to a 9x13-inch baking dish. Cover with foil and bake until warm, about 45 minutes. Remove from oven and serve warm.