Peel and finely chop the onion. Clean, wash, quarter and seed the tomato. Cut the flesh into fine cubes. Clean the lettuce and wash thoroughly. Roast hazelnut leaves without fat
Wash the fillet, dab dry and cut into about 12 thin medallions. Heat the oil. Fry the medallions for about 2 minutes on each side. Season with salt and pepper. Take them out, keep warm if necessary
Fry the onion cubes in the frying fat until golden brown. Deglaze with 2 tablespoons of water and vinegar. Season with salt, pepper, mustard and 1 pinch of sugar
Arrange lamb's lettuce and medallions on plates. Pour marinade over them. Sprinkle with diced tomatoes and hazelnuts. Serve with the baguette
Drink: cool white wine spritzer