Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: In a large skillet, cook the breakfast sausage over medium heat, breaking it up with a spoon until fully browned. Drain any excess grease and set aside.
Step 3: In a large bowl, whisk together the eggs, milk, salt, and pepper until well combined. You want a consistent, frothy mixture.
Step 4: Arrange 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 evenly over the layer of tater tots.
Step 6: Distribute 1 1/2 cups of the shredded cheese (1 cup cheddar, 1/2 cup Monterey Jack) over the sausage layer.
Step 7: Pour half of the whisked egg mixture evenly over the layers in the baking dish.
Step 8: Repeat the layers: top with the remaining tater tots, then the remaining sausage, and then the remaining 1 1/2 cups of shredded cheese (1 cup cheddar, 1/2 cup Monterey Jack). Pour the rest of the egg mixture over everything.
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 Tater Tot Breakfast Casserole is golden brown, the tater tots are crispy, and a knife inserted into the center comes out clean, indicating the eggs are fully set.
Step 11: Let the casserole rest for 5-10 minutes before slicing and serving. Garnish with fresh chives or green onions if desired.