Cook the ground beef and onion in a pot on medium heat, stirring often to prevent large chunks.Meanwhile, cut the crust off of the bread slices (save for stuffing or bread crumbs). Use a rolling pin to roll the bread slices flat and set aside. When all of the liquid has cooked out of the beef, add the can of mushroom soup and mix well. Finally, layer twice in a lasagna pan as follows:
- bread slices (butter the bottom layer to prevent sticking)
- ground beef mixture
- grated cheese
Cover with foil and bake at 425°F for 25 minutes. Cool for 10 minutes before serving.