Clean and wash kohlrabi, radishes and spring onions. Cut kohlrabi into sticks, radishes into slices and spring onions into rings. Clean and wash the salad and cut into bite-sized pieces. Stir buttermilk and crème fraîche until smooth. Season to taste with lemon juice, salt, pepper and a little sugar. Cut cress leaves from the stems with scissors and add to the dressing. Arrange the salad ingredients on plates, add the dressing