1. Grease a 9×13-inch baking dish with butter or cooking spray.

2. Cut the refrigerated biscuit dough into 1-inch pieces and scatter evenly over the bottom of the prepared baking dish.

3. In a large skillet over medium heat, cook the breakfast sausage until browned and cooked through, breaking it into small crumbles. Drain excess grease.

4. Add the diced yellow onion and red bell pepper to the skillet and cook until softened, about 3–4 minutes. Stir in the minced garlic and cook for 30 seconds, then remove from the heat.

5. Spoon the sausage and vegetable mixture evenly over the biscuit pieces in the baking dish.

6. In a large mixing bowl, whisk the eggs until well combined. Add the whole milk and heavy cream and whisk until smooth.

7. Season the egg mixture with kosher salt, black pepper, smoked paprika, dried thyme, and hot sauce if using, and whisk again to evenly distribute the seasoning.

8. Sprinkle most of the shredded cheddar and mozzarella cheese over the sausage and biscuits, reserving a small handful of each cheese for the top.

9. Slowly pour the egg mixture evenly over the contents of the baking dish, making sure it seeps down between the biscuit pieces. Gently press down any biscuits that are sticking up so they are lightly submerged.

10. Top with the remaining cheese and a sprinkle of sliced green onions.

11. Cover the baking dish tightly with plastic wrap or foil and refrigerate for at least 4 hours or up to 12 hours overnight.

12. When ready to bake, remove the casserole from the refrigerator and let it sit at room temperature while you preheat the oven to 350°F (175°C).

13. Uncover the casserole and bake for 40–45 minutes, or until the center is set, the eggs are no longer jiggly, and the top is golden and bubbly.

14. Let the casserole rest for 10 minutes before slicing. Garnish with extra green onions and serve warm with additional hot sauce if desired.