Cook the beetroot tubers whole in lightly salted water for about 1 hour. Then pour off the water, wipe off the skin with your hand (with rubber gloves) and puree it in a container.
Melt the butter in a small saucepan over medium heat and simmer until the solid whey pieces separate from the liquid butter and the butter is browned. Run through a filter so that the brown particles are removed.
Now gradually add the brown butter to the beetroot puree, puree again and season with nutmeg, salt and pepper.