Blend the olives, the garlic, a little oil and the anchovies on high speed to make a thin cream. Brown the onion and then the radicchio in a pan with a little oil. Cook the pasta in plenty of boiling, salted water. Drain quickly, retaining a little of the cooking water. Sauté the pasta in a pan with the radicchio, and then pour the olive pesto sauce on top. Mix well so that the sauce blends with the pasta. Spoon the warm yoghurt seasoned with salt and pepper on a plate, decorate with radicchio leaves and pour the seasoned hot pasta on top. Sprinkle with fresh, chopped aromatic herbs.