Fry the bacon, egg and mushrooms in a frying pan until the bacon is crisp, then set aside.
Butter the bread slices on one side. Add one slice of bread, butter side down, to the frying pan. Pile up the tomato slices, bacon, egg and mushrooms. Top with the other slice, buttered-side up.
Cook the toastie for 2–3 minutes over a medium heat until the botto