Non stick spray an 8" X 8" oven safe pan/casserole dish.
Remove breakfast sausages from casings and break up sausage meat with a fork.
Pan fry until no longer pink - but not too crispy breaking appart the bigger bits.
In a separate pan - melt butter and saute the onions for approx 3 mins - until they just begin to be opaque - add the hashbrowns and fry for approximately 5 - 6 minutes stirring frequently for even cooking.
In a bowl - combine the eggs, milk, mustard and salt and pepper (and/or any seasonings you like).
When your hashbrowns are done - put them evenly on the bottom of your casserole dish. Then layer the bread cubes. Next comes the sausage meat - distribute it evenly over the bread bits. Now pour the milk and eggs over the entire dish. Top with cheese. Bake for 50 minutes. Remove from oven and allow to cool for 10 minutes before cutting into it.
This recipe serves 4 people - one large piece each. This meal is filling and can very easily be doubled. Try other cheeses for deeper richer flavors.