In a food processor grind the sausage with a few pulses to make about 3 cups. Remove and set aside. Pulse the sourdough bread to create soft crumbs. Set aside
In a large skillet, heat the olive oil over medium heat. Add the chopped onions, celery and bell pepper. Cook until the onions are brown but not burned 8-10 minutes.
Add the andouille and garlic. Cook until the sausage is browned, 3-5 minutes.
Add the stock and hot pepper sauce and simmer about 10 minutes. Stir in the bread crumbs and remove from the heat.
Transfer to an 8 inch square baking pan. Optional make ahead prep: cover with foil or plastic wrap and refrigerate overnight.
Preheat oven to 425°F, bake uncovered for about 30-35 minutes until browned on top.
Notes
For true Cajun flavor, use a Louisiana hot sauce such as Tabasco, Crystal, Frank's, Red Rooster, etc. Start with 1-2 teaspoons unless you know you want it hot.