Peel and finely chop the onion. Heat the oil in a pot and fry the onions in it until transparent. Deglaze with the broth and add the peas. Let it boil for 5 minutes. Puree with the cutting stick of the hand mixer and season with salt and pepper.
Let it cool down. Clean and wash the radishes and cut into fine strips. Remove basil leaves from the stalks and cut into strips. Arrange soup in plates. Add a tablespoon of sour cream, radish sticks and basil strips to each plate.