Wash potatoes thoroughly and cook in boiling salted water for 12-14 minutes. Wash the rosemary and shake dry. Remove from 2 sprigs of needles. Shorten remaining twigs a little if necessary. Put rosemary needles and oil in a mortar and crush.
Pour the potatoes into a sieve and drain well. Press potatoes with the palm of your hand a little bit flat. Place 2 potatoes on top of each other and fix with wooden skewers. Place them on a baking tray lined with baking paper and sprinkle with rosemary oil.
Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 20-25 minutes until golden brown.
Wash the lemon hot, grate dry and grate the peel thinly. Mix lemon zest, sea salt and pepper. Remove potatoes from the oven. Carefully remove wooden skewers and put rosemary twigs into the potatoes instead of the wooden skewers.
Place potatoes on a plate and sprinkle with lemon mixture.