½tspcoarse Kosher salt(if using table salt, use half the amount)
½tspcoarse ground pepper
Preheat the oven to 350 F. Spray a 9-inch baking dish with non-stick baking spray.
In a large skillet over medium heat, cook the sausage until browned, breaking it up with a spoon. Use a slotted spoon to transfer the sausage to a bowl lined with a paper towel to absorb excess grease.
Add the diced onion and the frozen hash browns to the leftover grease in the skillet, cooking them until the hash browns begin to brown.
Spread the sausage into an even layer in the baking dish, then add the onions and hash browns. Sprinkle with the cheese.
In a bowl, whisk together the eggs, milk, salt and pepper until smooth, then pour the egg mixture over the hash browns.If there doesn't seem to be enough egg mixture, you can whisk 2 additional eggs with 1/4 cup milk to add to the casserole.
Bake the casserole, uncovered, for about 35-45 minutes, until the casserole is puffed and set, and a knife inserted in the center comes out clean.