Peel and dice the turnips into large cubes. Heat a pot of salted water to a boil. Add the turnips and let them boil for 1-2 minutes until tender.
Remove the turnips, and season them, while they are still warm, with the vinegar, rapeweed oil, mustard, salt and pepper.
Rinse the parsley and ground elder, dry both lightly in a dish towel, slice coursely and add the turnips.
Mix well and sprinkle with elderberry flowers.
Serve the turnips with the leg of lamb.