Preheat your Blackstone griddle to medium-high heat.
Oil the griddle, spread it evenly, then add the butter to melt. Add the chopped garlic, onions, and celery, stirring frequently until they begin to soften.
Add the sausage to the griddle. Break it apart and mix it with the vegetables. Cook until the sausage is browned and the onions and celery are fully tender.
Add the sourdough bread cubes to the mixture on the griddle, tossing to combine.
Transfer everything to a cast iron pan or Dutch oven. Stir in the rosemary, sage, thyme, garlic powder, black pepper, salt, chicken broth, and beaten eggs until fully combined.
Bake in a Blackstone pellet grill, smoker, or conventional oven at 400°F for 30–45 minutes, or until the top is lightly browned.
