Finely dice the shallots and fry in the butter. Pour in 100 ml of champagne and let it boil down a little. Add the chicken stock and cream and reduce the liquid by half. Pour through a sieve. Add the three types of mustard and season the soup with salt, pepper and the remaining champagne.
Clean the scallops and fry them in the olive oil for about two minutes on each side. Season with salt and pepper.
Foam the soup with a hand blender, place in preheated plates or soup bowls and serve with a freshly fried scallop and a little chervil.