Wash the liver, dab dry and cut into bite-sized pieces. Heat 2 tablespoons of oil in a frying pan and fry the liver for 5-6 minutes over medium heat. Season with salt and pepper.
In the meantime, clean, wash and drain the salad and possibly pluck into bite-sized pieces. Wash, dry and halve the tomatoes. For the vinaigrette, peel and finely dice the onion. Chop the pistachios.
Mix vinegar, mustard, onion and pistachios. Beat the remaining oil into it and season with salt, pepper and sugar. Arrange lettuce, tomatoes and liver on plates and pour the vinaigrette over them.
Serve sprinkled with pepper from the mill as desired.