Chop the onion, red bell pepper, and green bell pepper into small, uniform pieces.
Cook sausage in a skillet over medium heat, breaking it up with a spoon. Ensure it’s fully cooked and drain off any excess grease.
In a large skillet, add olive oil and heat over medium heat. Add the chopped onion and bell peppers.
Sauté the vegetables for about 5-7 minutes, or until they are softened and slightly translucent. Stir occasionally to prevent burning.
Add the crumbled sausage back to the skillet. Stir everything together and cook for another minute or two, just to heat the sausage through.
Remove the skillet from the heat and set it aside.
In a large bowl, crack all 12 eggs.
Add the milk, salt, and pepper to the bowl with the eggs.
Whisk everything together vigorously until the eggs are well combined and slightly frothy.
Set the egg mixture aside for now.
Preheat your oven to 350°F (175°C).
Grease a 9×13 inch baking dish.
Place one tortilla in the bottom of the baking dish. You might need to trim it slightly to fit snugly.
Pour about 1/6 of the egg mixture over the tortilla, just enough to cover it lightly.
Sprinkle about 1/6 of the sausage and vegetable mixture over the egg-soaked tortilla.
Sprinkle about 1/6 of the cheddar cheese and 1/6 of the Monterey Jack cheese over the sausage and vegetables.
Repeat layers: tortilla, egg mixture, sausage and vegetable mixture, cheddar cheese, and Monterey Jack cheese. Do this until you have used all 6 tortillas.
Make sure the top layer is cheese!
Carefully place the baking dish in the preheated oven.
Bake for 30-40 minutes, or until the eggs are set and the cheese is melted and bubbly. The top should be golden brown.
To check if the eggs are set, gently insert a knife into the center of the bake. If it comes out clean, the bake is done. If there’s still some liquid egg on the knife, bake for a few more minutes.
Once the tortilla bake is done, remove it from the oven and let it cool for a few minutes before slicing and serving.
Slice the tortilla bake into squares or rectangles.
Serve warm.
Optional: Top with your favorite toppings, such as salsa, sour cream, avocado, and chopped cilantro.
Notes
Spice it up: Add a pinch of red pepper flakes to the egg mixture or use spicy sausage for a kick.
Add more vegetables: Feel free to add other vegetables to the filling, such as mushrooms, spinach, or zucchini.
Use different cheeses: Experiment with different cheeses, such as pepper jack, mozzarella, or Gruyere.
Make it vegetarian: Omit the sausage and add more vegetables or use a vegetarian sausage substitute.
Make it ahead: You can assemble the tortilla bake ahead of time and store it in the refrigerator overnight. Just add a few extra minutes to the baking time.
Freezing: This tortilla bake freezes well. Let it cool completely, then wrap it tightly in plastic wrap and foil. Freeze for up to 3 months. Thaw in the refrigerator overnight before reheating.
Reheating: Reheat leftover tortilla bake in the microwave, oven, or skillet.
For a lower-fat version: Use egg whites instead of whole eggs, and use low-fat cheese.
Don’t overbake: Overbaking will result in a dry and rubbery tortilla bake. Keep an eye on it and remove it from the oven as soon as the eggs are set.
Use good quality tortillas: The quality of the tortillas will affect the overall taste and texture of the bake. Look for tortillas that are soft and pliable.