Heat milk and butter. Let gherkins and capers drain, then cut finely all.
Pell potatoes, dice and bring to the boil in salt water until the potatoes are just tender, then drain. Mash potaotes and stir in milk-butter mixture until smooth. Fold in mustard, capers, gherkins und 2/3 of chives. Sesaon to taste with salt and keep warm.
Fill a large pan with 1l water and vinegar, then bring to the boil. Crack always 2 eggs into the pan, slide white over yolk with a skimmer. Remove after about five minutes, then repeat for other eggs.
Sprinkle potatoe puree with the rest of chives and serve with poached eggs.