Stir sour cream and cream cheese until smooth. Cut cress from the bed. Stir about 3/4 of the cress into the cream. Season to taste with salt and pepper. Clean and wash the radishes. Cut into thin slices.
Cut the rolls in half. Cover each roll with a slice of salmon. Spread the radishes on top and put a blob of cream on each. Wash the sprouts and let them drip off. Sprinkle with remaining cress and sprouts. Add the rest of the cream
With 8 people: