Cut the roots off the fresh cale and remove any damaged portions. Cut the stems and leaves into small pieces. In a covered saucepan cook the kale in a large amount of boiling salted water for an hour. Drain well; squeeze out excess liquid.
While the kale is cooking, peel and quarter the potatoes and chop the onion. In a covered saucepan, cook the potatoes and onion in boiling salted water for 20 to 25 minutes or until the potatoes are tender. Drain well.
Just before the kale and potatoes/onion are done, melt 2 tbsp butter in a skillet and cook the knackwurst for 5 to 10 minutes or till heated through.
In a mixing bowl beat the hot kale, hot potatoes, and onion on low speed of an electric mixer until smooth. Beat in the 1/4 cup butter, salt, pepper, and nutmeg. Add as much light cream or milk as necessary to make fluffy (but not runny).
Place the vegetable mix on a serving dish and arrange the knackwurst around it. Garnish with shredded carrots.