Wash the chicken filet, dab dry and cut lengthwise into three. Mix lemon juice, zest and 1 tablespoon of oil. Season with salt and plenty of pepper. Marinate the meat for about 30 minutes.
Peel, wash and cut the potatoes into large pieces. Cover and cook in salted water for about 20 minutes.
Clean, wash and cut the leek into rings. Remove the meat from the marinade and let it drip off. Heat 1 tablespoon of oil in a large frying pan. Fry the meat for approx. 8 minutes, turning it over. Remove and keep warm. Add marinade and 100 ml water to the frying pan and bring to the boil. Pour the meat over the meat.
Heat 1 tablespoon of oil in a frying pan. Steam the leek for about 5 minutes. Season with salt and pepper. Warm up the milk. Drain the potatoes. Add milk to the potatoes and mash everything to puree. Season the puree with salt and nutmeg. Arrange pepper chicken, puree and leek.