Step 1: Preheat your oven to 350°F (175°C). A properly heated oven ensures that your casserole cooks evenly and thoroughly.
Step 2: In a large skillet over medium heat, cook the sausage until fully browned and crumbly, about 5-7 minutes. Drain excess fat and set aside to cool.
Step 3: In your greased 9x13-inch baking dish, arrange the frozen hash brown patties in a single layer.
Step 4: Spread the cooked sausage evenly over the layer of hash browns.
Step 5: Pour the salsa evenly over the sausage layer.
Step 6: Evenly sprinkle both the cheddar and Monterey Jack cheeses over the salsa layer.
Step 7: In a large bowl, whisk together the eggs, milk, and taco seasoning until well combined.
Step 8: Carefully pour the egg mixture over the layered ingredients in the baking dish.
Step 9: Place the casserole in the preheated oven and bake for 45-50 minutes, or until the eggs are set and the top is golden brown.
Step 10: Once baked, remove the casserole from the oven and let it cool for about 10 minutes before slicing.