Puree the crème fraîche with all the other ingredients up to and including the pepper, cover and chill.
Mix the breadcrumbs, fennel seeds, pepper and chives, transfer to a plate. Empty the flour onto a plate, beat the egg in a deep plate. Toss the mushroom slices in the flour and shake off the excess. Dip the mushrooms in the egg and then in the breadcrumbs, press firmly on the crumb coating. Heat a little clarified butter in a non-stick frying pan. Fry the mushrooms in batches for approx. 1 min. on each side, drain on kitchen paper, season with salt. Serve the mushrooms with the dip.