1-Getting started with this breakfast casserole is straightforward and fun, especially if you’re new to cooking. Begin by preheating your oven and gathering your ingredients to make the process smooth and enjoyable. our guide to egg substitutions can help if you need to make changes for dietary reasons.

2-First, grease a 9×13-inch or similar oven-safe dish and arrange the 4 cups of bread cubes evenly at the bottom. Heat 1 teaspoon of olive oil in a large skillet over medium heat, then add 1 pound of ground pork sausage (casings removed) and 1 teaspoon of dried rosemary or Italian seasoning if using, breaking it into bite-size pieces as it cooks.

3-Stir in 3/4 cup of chopped yellow onion, 2 garlic cloves (minced), 2 cups of chopped bell peppers, 1 cup of sliced mushrooms, and 1 cup of roughly chopped fresh spinach. Cook until the vegetables are slightly softened and the sausage is mostly cooked, about 5-6 minutes, then remove from heat and spread evenly over the bread cubes.

4-In a separate bowl, whisk together 12 large eggs, 1/4 teaspoon of salt, 1/8 teaspoon of freshly ground black pepper, 2/3 cup of milk or half-and-half, and 1 cup of shredded cheddar cheese. Pour this mixture evenly over the sausage and vegetables, adding extra salt and pepper on top if desired.

5-Cover the dish with plastic wrap or foil and refrigerate for at least 30 minutes and up to 24 hours. Let it sit at room temperature for 10-15 minutes before baking, then preheat the oven to 375°F (191°C) and bake uncovered for 40-45 minutes, or until the top is golden and a toothpick inserted in the center comes out clean. Allow the casserole to cool for 10 minutes before slicing and serving, with leftovers stored in the refrigerator for up to 5 days.