Preheat your oven to 180°C (350°F). Grease a small baking dish.

Cut the bread slices into cubes, about 2-3 cm (1 inch) thick. Arrange them in the bottom of the prepared baking dish.

Heat the oil or butter in a frying pan over medium heat. Add the diced sausage and cook until browned.

If using onion, add it to the pan with the sausage and cook until softened, about 3-5 minutes.

Scatter the cooked sausage (and onion, if used) over the bread cubes in the baking dish.

In a bowl, whisk together the eggs, milk, salt, and pepper.

Pour the egg mixture evenly over the bread and sausage in the dish, making sure most of the bread is covered.

If using cheese, sprinkle it evenly over the top.

Bake for 20-25 minutes, or until the egg is set and the top is golden brown.

Let it rest for a few minutes before serving hot.