In a bowl, combine the sausage, hash browns, onion and 1/2 cup cheese.
Spoon into 12 greased muffin cups.
In the same bowl, whisk the eggs, milk, biscuit mix, pepper and salt.
Pour over sausage mixture in muffin cups.
Bake at 400 degrees F for 15-20 minutes or until set.
Sprinkle with remaining cheese.
Bake 2-3 minutes longer or until cheese is melted.
Let stand 5 minutes before serving.