Cut off one end of the loaf. With a long, sharp knife, cut all round the inside of the loaf 1 cm (1/2) inch from the crust and, using your hand, scoop out the bread from inside.
Place the butter in a bowl and beat until light and creamy.
Shell the hard-boiled eggs, cut them in half and remove the yolks.
Sieve the yolks into the butter and mix well.
Finely dice the egg whites and the carrot.
Drain the mushrooms and chop finely, together with the ham, spring onion and capers.
Stir all the chopped ingredients into the butter mixture, followed by the sliced olives.
Season with celery salt, salt and pepper. Spoon the mixture into the loaf, filling it completely, and pressing down so that no spaces are left.
Replace the piece originally sliced off, wrap the loaf in kitchen foil and leave to stand for a few hours in the refrigerator.