Brown Italian sausage on medium heat in a large pan. Remove from pan and set aside and drain on paper towel
Saute the onion, carrots, garlic, celery, and mushroom until translucent and tender. Remove from pan. Add to sausage and let cool.
Break up saltines into a large bowl. Add warm water and let them soak for 30 seconds MAX. They should soak up the water and get soft then quickly squeeze out any excess.
Combine everything into the bowl with the sausage, vegetables with one egg, beaten. Add to a buttered baking dish.
Bake at 350 degrees for about 30-40 minutes until golden brown.