Step 1: Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.
Step 2: In a large skillet, cook the breakfast sausage over medium heat, breaking it up into crumbles as it browns. Drain any excess grease.
Step 3: In a large bowl, whisk together the eggs, milk, salt, and pepper until well combined. For an extra creamy casserole, you can add a splash of heavy cream or a tablespoon of cream cheese.
Step 4: Spread half of the frozen tater tots in an even layer at the bottom of the prepared baking dish.
Step 5: Sprinkle half of the cooked sausage over the tots, followed by half of the shredded cheese (cheddar and Monterey Jack).
Step 6: Pour half of the egg mixture evenly over these layers.
Step 7: Repeat the layering with the remaining tater tots, sausage, and cheese.
Step 8: Pour the remaining egg mixture evenly over the top layer.
Step 9: Cover the baking dish loosely with aluminum foil and bake for 30 minutes.
Step 10: Remove the foil and continue baking for another 20-30 minutes, or until the casserole is golden brown, the tots are crispy, and a knife inserted into the center comes out clean, indicating the eggs are fully cooked.
Step 11: Once out of the oven, let the casserole rest for 5-10 minutes before slicing and serving. Garnish with fresh chives, green onions, or a dollop of sour cream or salsa if desired.