Boil half the potatoes with skin in boiling water for about 20 minutes. Drain, rinse with cold water and peel. Mash the still hot potatoes with a potato masher. Let them cool down.
Wash the rosemary and dab dry, remove the needles and chop finely. Mix wheat and spelt flour, baking powder, rosemary, except for 2 tbsp, 1 1⁄2 tsp salt and 1 tsp paprika in a large bowl.
Remaining potatoes peel, wash and finely grate. Squeeze the grated potatoes. Add grated and mashed potatoes and milk to the flour. Knead first with the dough hooks of the mixer, then with your hands to a smooth dough.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Line baking tray with baking paper. Form the dough into a round loaf on a floured work surface and place on the baking tray. Make a round cut in the surface with a sharp knife.
Sprinkle with sea salt and the rest rosemary. Bake in a hot oven for 50-55 minutes. Cover after about 45 minutes if necessary. Let it cool down on a cake rack.