Wash triplets thoroughly and quarter them. Halve the garlic bulb. Peel onions and cut into slices. Put potatoes, onions, garlic and sausages in an ovenproof dish. Season with salt and pepper. Cook in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see manufacturer) for approx. 45 minutes.
Wash the tomatoes and pluck them from the panicles. Wash the rosemary and shake dry. Strip needles from the twigs. Approximately 15 minutes before the end of the cooking time, add the tomatoes and rosemary and finish cooking the potato and sausage mixture.
Wash the lemon hot, dab dry and rub the peel. Mix the sour cream and the lemon peel. Season with salt and pepper. Remove the oven chorizo and serve. Serve with lemon sour cream.