Put a layer of the potato slices in the bowl and season with salt and pepper. Then some of the cucumbers and the apple, then again potato slices and then season them again vigorously, etc.
Finally, distribute the glass of tartar sauce over the salad and add plenty of pickle water. Stir gently.
Put the lettuce in the fridge to steep.
Warning: the potatoes soak up a lot of liquid (read: sauce). That`s why I still pour a little milk into the empty tartar sauce jar, close it and put it in the fridge. When I serve the salad, I shake the tartar sauce glass again vigorously (then the milk with the remains of the tartar sauce will be a bit spicy) and then pour it over the salad!