Wash the maties briefly and place them in the cold milk for 1/4 to 1/2 hour (depending on salt content). Wash potatoes thoroughly and cook in boiling water for 15 to 20 minutes. Finely dice bacon.
Peel and chop the onion. Cut the cress short. Wash lemon hot, dab dry and grate the peel. Drain potatoes, quench briefly and peel the skin. Leave bacon in a pan without fat until crispy.
Briefly sauté the onion and lemon peel. Add cress and toss the potatoes in it. Dab the maties dry and serve with the potatoes.