Wash potatoes thoroughly, cut into slices. Heat oil in a large pan. Fry potatoes vigorously for about 25 minutes, turning. Cut feta into cubes. Roll up the sausage slices individually and cut into small rolls.
Wash the marjoram, shake dry and pluck the leaves from the stalks. Season potatoes with salt, pepper and fennel. Add olives, marjoram, sausage and feta. Arrange on plates. Garnish with pepperoni.