Wash the potatoes well and boil for approximately 20 minutes until throughly cooked,, drain and peel immediately, slice.
Remove the rind from the cheese, mash with a fork and mix into a smooth paste with crème fraîche, mayonnaise and milk.
Peel the onions and slice into rings. Drain tomatoes and capers and cut the tomatoes into strips. Wash the lettuce, split into leaves and arrange on a plate.
Mix the potatoes with the other salad ingredients, pour the blue cheese dressing over the top and mix carefully.
Warm the Deutschländer according to the instructions on the jar and serve to salad garnished with parsley.