Set the washed potatoes in a casserole and cover with cold salted water. Cook until you can easily slip a knife in the center of a potato. Cool down right away.
Slice potatoes into quarters and set with radish in a large bowl. Set aside.
In a pan, cook chicken with butter at medium-high heat for 5 minutes. Reduce heat to medium, then add sliced leeks and garlic. Continue cooking for 5 minutes while stirring from time to time. Remove from heat.
Add the remaining ingredients to the chicken. Mix well and season.
Pour chicken preparation over potatoes and set aside. Stir at the least possible to avoid crushing potato quarters.