Marinade: Mix vinegar, mustard, salt and a pinch of sugar. Beat in the oil vigorously. Season to taste with cayenne pepper.
Wash the vegetables. Cut the leek into fine strips and the peppers into small cubes. Halve the olives. Drain the corn. Skin the sausage and cut into thin sticks.
Put the vegetables, sausage and marinade in the salad bowl and mix. Cover and leave to steep for 5-6 hours (preferably overnight). Season the leek salad again with salt and cayenne pepper. Garnish with parsley if desired.
Prep time: 30 minutes, waiting time: at least 5 hours