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Prep: Preheat your oven to 375°F (190°C). Generously grease a 9×13 inch baking dish.
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Cook the Sausage: In a large skillet over medium heat, cook the sausage, breaking it into crumbles with a spoon, until it’s browned and no longer pink. Drain off any excess grease.
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Layer the Base: Spread the thawed hash browns in an even layer at the bottom of the prepared baking dish. Scatter the cooked sausage crumbles evenly over the hash browns.
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Create the Creamy Egg Mixture: In a large bowl, whisk the eggs, milk, salt, and pepper together until smooth and well-combined. Add the softened cream cheese and whisk vigorously until the mixture is mostly smooth (a few small lumps are okay).
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Assemble the Casserole: Pour the egg and cream cheese mixture evenly over the sausage and hash brown layers. Gently shake the dish to ensure the liquid distributes throughout.
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Add the Cheese Topping: Sprinkle the shredded cheddar and mozzarella cheeses evenly over the top.
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Bake: Bake uncovered for 35-40 minutes, or until the center is fully set (doesn’t jiggle) and the top is golden brown and bubbly.
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Serve: Let the casserole rest for 5-10 minutes before slicing. This allows it to set for cleaner portions. Garnish with green onions or chives if desired, and serve warm.
 
Tips & Variations
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Vegetarian Twist: Simply omit the sausage. For added heartiness, sauté 1 cup of diced bell peppers and onions, or use a plant-based sausage alternative.
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Customize Your Casserole: Feel free to add in ½ cup of diced cooked bacon, ham, sautéed mushrooms, spinach, or jalapeños for a kick.
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Thawing Hash Browns: For the best texture, place frozen hash browns in the refrigerator overnight. For a quick thaw, spread them on a baking sheet in a single layer for 30-60 minutes.