Cut 7 portions of approx. 60 g each from the potato dough. First shape each into a ball, plate them lightly and place a lightly heaped teaspoon of onion sausage in the middle. Cover this with the potato mixture and roll it back into a ball. In the meantime, bring enough salted water to the boil in a large saucepan, add the dumplings, turn the heat down halfway and let them simmer for about 10-15 minutes. When they rise to the surface, they are done.
While the dumplings are cooking, heat the butter in a saucepan large enough for the kohlrabi and stir in the flour. This continues until the two have combined and a white film forms on the bottom of the pot while stirring. Then - also while stirring with a whisk - deglaze the butter and flour mixture with the kohlrabi sauce and - while still stirring - bring it to the boil until creamy. Then stir in the sour cream and season the sauce with salt, pepper and nutmeg. Reduce the heat to a minimum, add the pre-cooked kohlrabi, mix well with the sauce and heat it in it and let it simmer a little.
While the kohlrabi is brewing and the dumplings are in the hot water, melt the butter in a pan and stir in the breadcrumbs. Then turn the heat down a little and roast the crumbs until golden brown while stirring several times. When they are ready, lift the dumplings to be served out of the water with a sieve ladle, drain very well and immediately toss in the breadcrumbs and coat all around with them.
Then serve with the kohlrabi and decorate with a little chopped parsley ... a quick family meal is ready.