Wash untreated orange thoroughly and finely grate half of the peel. From the other half peel in fine stripes with a julienne nipper. Peel all oranges so that the white skin is completely removed.
Remove the fillets with a sharp knife between the parting skins. Squeeze the juice out of the parting skins and collect it in a bowl. Mix yoghurt, orange peel, orange juice and salad cream. Season with salt, pepper and sugar.
Peel and finely chop the onion. Clean and wash the lamb's lettuce and drain well. Clean, wash, drain and tear radicchio. Mix salad, oranges and onion. Arrange in four small bowls or plates, spread yoghurt-orange cream over them and garnish with orange julienne.