Wash the potatoes well and place them in their skins in an ovenproof dish. Sprinkle lightly with salt and roast in the oven at 200 °C for 40 to 50 minutes, depending on size. Potatoes can also be cooked wrapped in aluminum foil. While still hot, cut the potatoes into slices and arrange in portions on preheated plates in the shape of a fan, season with a little salt. Place a small heap of caviar in the center of each fan. Mix sour cream with finely chopped spring onions and chopped dill and drape around the caviar. Garnish with a few sprigs of dill before serving.