Radish soup with yoghurt and radish leaf oil

After an overindulging weekend I wanted something very light for today's lunch. As I anyway bought too many bunches of radish on the market, I wanted to make something that needs a lot of them. I have had the idea of radish soup already for a while on my mind, but I always postponed it. I definitely wanted to cook the radish, but it was important to keep its colour, therefore I prepared a stock using potatoes and then I used that to cook the radish for a few minutes. During the morning walk I collected some ramson flowers, ground ivy, yellow archangel, henbit deadnettle that brought spring right onto the plate.

Ingredients:
300 g potatoes
1 onion
1 bay leaf
1/8 teaspoon caraway seeds
2 teaspoon butter
500-700 ml vegetable stock
1 bunch radish
125 g yoghurt
3-4 tablespoons rapeseed oil
salt, pepper

Peel and cut potatoes in cubes. Sautee chopped onion in a teaspoon butter, add diced potatoes, bay leaf, caraway seeds and vegetable stock. Cook over low heat for 15-20 minutes. Now sieve and set the liquid aside. You won't  need the cooked potatoes for the soup, but do not throw away, instead make a puree or use in some kind of yeast dough that needs cooked potatoes. Sautee sliced radish in the other teaspoon of butter, add the potato liquid and cook for 2-3 minutes. Pour the soup into a mixer, add yoghurt and puree, season with salt and pepper. If you want a really smooth soup sieve. Serve the soup either lukewarm or chilled. For the oil puree about 1/4 of the radish leaves with the rapeseed oil.