1 Preheat the oven's broiler. Cut the cheese slices in half. Soak the bread in lukewarm water. Peel the onions and garlic and chop finely. In a pan, heat 1 tablespoon oil and sweat the onion with the garlic until translucent. Remove from the heat, allow to cool and mix with the minced meat, mustard, squeezed-out bread and egg and season with salt and pepper.
2 Form 12 small balls from the mixture, flatten into patties and cook until brown in hot butter. Remove, top with cheese and melt under the broiler. Meanwhile, peel the onion, cut into strips and fry until golden brown in another pan with the remaining oil. Add the tomato paste and ketchup, cook briefly, then deglaze with the broth.
3 Season with salt, pepper, chili powder and sugar and simmer until slightly creamy over medium heat. Cut the mini hamburger buns in half crosswise, toast and distribute a hamburger, sauce, 1-2 cucumber slices and cress leaves on the buns. Place the top of the bun on the burger and secure 3 stacked mini burgers with a wooden skewer. Serve each garnished with a cherry tomato.