Bake the potatoes until tender. Scoop out the centres and rub through a sieve. Put the sieved potato into a pan with the butter, cream and seasoning. Stir over a brisk heat until the mixture amalgamates and does not stick to the pan.
Remove from the heat, cool a little and then add the egg yolks and the whipped egg white. Shape into the size you want and poach for 5 minutes or so in boiling water with a little salt added. Drain and serve.