Line a cookie sheet with parchment paper and add the cubed bread. Toast in the oven for 15-20 minutes.
While the bread is toasting, place a large nonstick frying pan over high heat and add the butter, onion, and celery. Saute for 10 minutes, or until tender. Pour into a large bowl.
Use the same frying pan to brown the sausage, then add to the bowl.
Add the toasted bread to the bowl, along with the salt, pepper, rosemary, and stock.