Soak the buns. Peel and finely chop the onion. Knead minced meat, squeezed out roll, onion and egg. Season with salt, pepper and mustard. Shape into dumplings with wet hands. Let them simmer in plenty of boiling salt water for about 12 minutes.
Then pour the stock through a fine sieve and measure 1/2 litre. For the sauce melt the fat. Sweat flour in it. Add the stock while stirring constantly, let it simmer for about 5 minutes. Mix 3 tablespoons cream and egg yolk.
Heat the remaining cream in the sauce. Drain the capers and add them to the sauce. Season to taste with salt, pepper and lemon juice. Stir in whisked egg yolk. Do not let it boil any more! Heat the dumplings in the sauce.
Arrange the dumplings in portions sprinkled with chopped parsley. Garnish with lemon. Boiled potatoes taste good with it.