Peel off the skin of the potatoes and cut into half slices. Put in a deep plate. Finely chop the shallot and pour over the potatoes. Salt and pepper, then let steep for 5 minutes. Spread olive oil over it. Squeeze the lemon and add the juice. Do not stir.
Serve with bread or as a side dish to meat and fish (then it is neither vegetarian nor vegan).