Pass the liver and onion through a meat grinder. Add the egg, flour, milk and mix well. Add salt and pepper to taste.
Heat a frying pan with a little oil. Spoon out the liver mass and spread evenly throughout the pan. Fry with the lid closed on both sides until golden brown (about 2-3 minutes on each side), gently turning with a spatula.
For the omelet: whisk three eggs with milk. Fry on both sides.
Cut tomatoes into thin slices.
Combine the liver pie:
liver pancake, mayonnaise, omelet, mayonnaise, tomatoes. Repeat the layers, finishing with a liver pancake. Decorate as desired.