1. slice blue cheese as thinly as possible. Peel onion and slice into rings. Rinse and clean the spring onions and cut crosswise into fine slices. Clean, rinse and grate the radishes. Sprinkle everything over the cheese.
Mix the vinegar with the mustard, salt and pepper, add the oil and pour the marinade over the cheese mixture. Let the salad marinate for at least 20 minutes. Later, rinse the watercress, shake dry, pluck the leaves from the stems and garnish the salad with them.