Brush the potatoes well and quarter them lengthways. Drizzle with oil and place with the cut surface facing up on a baking sheet lined with baking paper. Mix the paprika powder, salt, sugar and cayenne pepper and sprinkle half of it over the potatoes. Bake in a preheated oven at 200 ° C for about 20 minutes.
After about 10 minutes of cooking, place the tomatoes with the cut surface facing up to the potatoes, sprinkle the remaining seasoning mixture over them.
In the meantime, stir together the herb quark, sour cream, horseradish and chives, season with salt and pepper. Serve with the potatoes and tomatoes.