1 large loaf Italian or French bread
1 Tbs olive oil plus more to grease baking dish
12 oz Italian sausage, casings removed
1 yellow onion, diced
1/2 tsp freshly ground black pepper
1/4 tsp dried oregano
1/4 tsp dried thyme
1/8 tsp dried rosemary
1 pinch cayenne pepper
1 lb baby spinach
12 large eggs
2 tsp kosher salt
4 cups milk
8 oz fontina or fontal cheese, shredded
Step 1: Cut bread into 1-inch cubes and spread out in a single layer on the work surface; leave uncovered overnight to become stale.
Step 2:
Add olive oil to a skillet set over medium-high heat and add sausage. Cook, while crumbling with a spatula, for a few minutes, just until the sausage starts to brown. Add onions, a large pinch of salt, black pepper, cayenne, oregano, thyme, and rosemary. Cook, stirring until the onions soften and start to turn translucent.
Step 3: Transfer the mixture into a bowl, then spoon about 1 tablespoon of rendered sausage fat back into the pan; place pan back over medium-high heat.
Step 4: Add spinach and cook, tossing with tongs until barely wilted and bright green. Transfer into a strainer to cool. Squeeze out any excess water and chop before using. Or use scissors to snip into small pieces.
Step 5: Whisk eggs with salt until yolks have been incorporated into the whites. Whisk in milk and set aside.
Step 6: Grease a 9×13-inch casserole dish with olive oil. Cover the bottom with a single tight layer of stale bread cubes. Top evenly with about 60% of sausage mixture, layer on 60% of spinach, and then scatter over half the cheese.
Step 7: Top this with another layer of bread cubes, pressing down lightly with your hands to flatten. Top bread with remaining sausage and spinach. Ladle egg and milk mixture evenly over casserole. Top with the remaining cheese.
Step 8: Wrap tightly and place in the refrigerator overnight.
Step 9: Preheat oven to 350 degrees.
Step 10: Bake strata in the preheated oven until top is lightly browned, and an instant read thermometer inserted into the center reaches 150 degrees, about 1 hour 15 minutes.
Step 11: Let strata rest for 10 to 15 minutes before serving.
