Cut the bacon in shreds crosswise, using the shears for this purpose. Cook bacon with the butter about ten minutes, without scorching bacon. Remove scraps of bacon, add the peas, onions and mint. Cook until peas and onions are soft, adding one-fourth cup boiling water to prevent scorching. Beat the yolk slightly, add the cream and lettuce cut in quarters, season with salt and pepper. Let boil up once and serve.