Soak toast in cold water. Peel and finely chop the onion. Put minced meat, egg, half of the onion cubes, some salt and pepper in a bowl. Squeeze the toast well, add it and knead well with the dough hooks of the hand mixer.
Mix in the capers. Place the roulades on a kitchen board, spread with the chopping mass and roll up. Fix with wooden skewers or roulade needles. Heat the oil in a frying pan or casserole and fry the roulades while turning.
Season with salt and pepper, add remaining onion cubes. Pour in broth, bring to the boil, cover and stew for about 30 minutes. In the meantime peel, wash and cut the potatoes into pieces. Cook in little boiling salted water for about 20 minutes.
Wash parsley, dab dry and chop except for something to garnish. Remove the finished roulades from the stew stock and keep warm. Stir the lemon zest and sour cream into the stock, bring to the boil and pour in the sauce thickener while stirring.
Season the sauce with lemon juice, salt and pepper. Add the roulades to the hot sauce. Drain the potatoes, let them evaporate and toss them with the parsley. Wash the lemon thoroughly and remove half of the peel in fine strips with a pestle ripper.
Arrange roulades and potatoes on plates, sprinkle with lemon zests. Garnish with caper apples and parsley. Serve with pickled beetroot.