Easy Breakfast Slices

1. Prepare the Sausage Mixture: The night before, cook the sausage and chopped onion in a nonstick skillet over medium-high heat until the sausage is browned and fully cooked. Drain any excess grease and set aside to cool.
2. Combine Ingredients: In a large mixing bowl, whisk together the eggs, egg whites, milk, mustard, salt, and pepper. Add in the bread cubes, cheese, and cooled sausage mixture, stirring until everything is well coated. Pour the mixture into a 13x9-inch baking dish lightly sprayed with cooking oil. Cover and refrigerate overnight.
3. Bake: Take the dish out of the refrigerator about 30 minutes before baking. Preheat your oven to 175°C (350°F) and bake, uncovered, for 35 to 40 minutes, or until a knife inserted into the centre comes out clean.

Enjoy your Easy Breakfast Slice!