Wash the potatoes thoroughly, cleaning them with a brush if necessary. Peel and roughly dice the onion. Clean, wash and slice the pepperoni into thin rings. Wash the rosemary, dab dry and pluck the needles from the twigs.
Roughly dice the potatoes. Mix the potatoes, onion, pepperoni, 5 tablespoons of olive oil and half the rosemary, season with salt and pepper. Put them into the fat pan of the oven. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 40-45 minutes.
10 minutes before the end of the baking time add olives and the remaining rosemary. Crumble the feta cheese. Remove potato vegetables from the oven and arrange on a plate. Crumble feta cheese over it. Drizzle with 1 tablespoon of olive oil and serve.