Red lentil puree with mint yogurt

For 6. Slice 2 small onions and 2 carrots and sweat them in a mixture of oil & butter until tender. Toast coriander and caraway seeds in a hot pan (app. 2 tbs of each), grind. Add half the spices to the onions, stir 2 minutes, then add 350 g of red lentils and 1.5 l of liquid (water or a mixture of water and bouillon). Bring to a boil, lower the heat and simmer for 15 minutes. Puree, adding water if necessary. Return to the heat, add the remaining spices, and serve with plain yogurt mixed with fresh, chopped mint leaves.