Chop the carrots and potatoes into small pieces. Braise both in 2 tablespoon butter. Deglaze with vegetable stock and simmer over low heat, then puree. Add the rest of the butter until you have a thick soup. While the vegetables are simmering, the egg custard can be prepared. To do this, whisk the eggs with the milk, add the chives and the spices. Let the egg mixture freeze in a microwave oven at around 600 watts. Then add this in cubes, strips, etc. to the soup.