How to make
Prepare a blend of finely chopped onion, minced meat, finely chopped mushrooms, black pepper, salt and mustard. Mix well.
Distribute the resulting mixture evenly over the bread slices, then coat them with the beaten egg. Put the slices in a buttered baking dish and bake in a hot oven until browned.
Sprinkle them with grated cheese and bake until softened.
