Grease a baking dish with 1 tbsp butter or cooking spray and set aside. If using fresh white sandwich bread cut into 1-inch cubes, spread the cubes on a baking sheet and let them sit out for 30–60 minutes to dry slightly, or toast at 300°F for 10 minutes. Slightly stale 6 cups white sandwich bread cut into 1-inch cubes absorbs the custard better without getting soggy.

Pull sausages from the refrigerator about 10 minutes before cooking — cold links cook unevenly. Pat casings dry with a paper towel; surface moisture causes steaming instead of searing. Keep fresh links whole — do not pierce the casings or fat and juices escape, leaving dry sausage. Have an instant-read thermometer ready; visual cues alone won't confirm doneness.

Heat a medium to large skillet over medium to medium-high heat. Add a little oil if the pan isn't nonstick. Lay links in a single layer with at least 1 inch of space between them — crowding causes steaming, not browning. For fresh raw sausages: Add 1/4 inch of water, bring to a simmer over medium-high (about 5 min), then reduce to medium, cover, and cook until an instant-read thermometer reads ~130°F, about 6–8 min. Uncover, raise heat to medium-high, and cook turning occasionally until water evaporates and casings are deeply browned on all sides, about 8 more minutes. Total time: 10–16 min depending on link size. For pre-cooked or smoked sausages: Heat oil or butter over medium-high and cook, turning occasionally, until browned and heated through, about 5 min. No raw internal temp target needed — just color and warmth.

Spread the 6 cups white sandwich bread cut into 1-inch cubes cubes evenly across the bottom of the prepared baking dish. Scatter the 1 lb breakfast sausage bulk pork sausage and vegetable mixture evenly over the 6 cups white sandwich bread cut into 1-inch cubes. Sprinkle 1½ cups of the shredded 2 cups shredded cheddar cheese sharp cheddar recommended over the top, reserving the remaining ½ cup for later.

In a large mixing bowl, whisk together the 8 eggs large, 2 cups whole milk, 1 tsp dry mustard powder, ½ tsp garlic powder, ½ tsp onion powder, ¾ tsp kosher salt, and ¼ tsp black pepper freshly ground until fully combined and smooth.

Pour the egg custard evenly over the 6 cups white sandwich bread cut into 1-inch cubes, 1 lb breakfast sausage bulk pork sausage, and 2 cups shredded cheddar cheese sharp cheddar recommended in the baking dish. Gently press down on the 6 cups white sandwich bread cut into 1-inch cubes with a spatula or the back of a spoon to help it absorb the custard. Cover tightly with plastic wrap or aluminum foil.

Refrigerate for at least 30 minutes, or overnight (up to 12 hours). The longer it soaks, the more custardy and cohesive the final casserole will be.

When ready to bake, preheat your oven to 350°F. Remove the casserole from the refrigerator and let it sit at room temperature for 15–20 minutes while the oven heats up.

Remove the cover and sprinkle the reserved ½ cup of shredded cheddar cheese sharp cheddar recommended evenly over the top. Bake uncovered for 45 to 55 minutes, until the top is golden brown, the edges are set, and the center no longer jiggles when you gently shake the dish. A knife inserted in the center should come out clean.