A delicious, fresh, simple salad. If you are unable to find pear vinegar in the shops you can just as easily use apple cider vinegar or any other type of white vinegar that is slightly sweet.
Rinse the lettuce leaves and dry them well, preferably using a salad spinner.
Prepare the dressing: mix the vinegar, Dijon mustard, salt and oil in a jam jar, screw the lid on tightly and shake well.
Put the dressing on the salad just before serving.