Boil potatoes in their skins, peel and press through a potato ricer.
Knead with salt, egg and cornstarch. Brush baking sheet with 2 tablespoons olive oil and sprinkle with 1 teaspoon rosemary needles.
Press the potato mixture evenly apart on the baking sheet.
Bake the potato base in the preheated oven at 200 degrees (convection oven at 180 degrees) on the 2nd shelf from the bottom for 20 minutes.
Wash and slice the tomatoes. Take out the baking tray and cover the bottom with tomato slices. Crumble feta cheese and spread over tomatoes with olives, oregano and parmesan.
Drizzle remaining olive oil over the top, season with pepper. Bake the pizza in the oven at the same temperature for another 25-30 min.