Place a 28 cm cake ring on a flat serving plate with a slightly curved edge. Prepare all vegetables before assembling: shred 1 head of lettuce; slice 1 cucumber thinly; finely slice 2 onions; slice 4 firm tomatoes; dice 2 bell peppers (yellow and green); slice 1 leek; hard-boil and slice 6 eggs; slice 1 bunch of radishes (reserving 4 whole for garnish); cut 8 boiled ham slices into small pieces; dice 3 mozzarella balls or crumble 1 block of sheep cheese.
Layer inside the ring in this order, pressing each layer very firmly before adding the next: lettuce, cucumber, onion, tomato, mozzarella/sheep cheese, egg, leek, bell pepper, ham, radish slices.
Spread 5 tbsp tartar sauce evenly over the top and sprinkle with 200 g grated cheese. Press down firmly once more to compact the cake.
Decorate the top with the reserved 4 whole radishes, a few ham rosettes, pickles, and egg slices. Cover with cling film and refrigerate overnight, until the layers set into a sliceable cake.
To serve, carefully lift off the cake ring. Slice into 16 wedges with a sharp electric or long-bladed knife, supporting each slice with a second cake server as you lift it out so the layers hold.