These are very soft pancake-like treats but made larger (approx twice the size) and more thinly than pancakes. They can be spread with butter and/or jam and are traditionally rolled up before eating (although this adds nothing to the flavour).
Beat the egg yolks and blend in the sifted flour, sugar, salt. Then add in the melted butter and milk to make a thin batter about the consistency of thin cream.
Beat the egg whites to the soft peak stage and quickly add to the batter, folding with a knife or metal spoon.
Heat a lightly greased gridle or a heavy frying pan and pour in large spoonfuls of the batter. Each crumpet should spread thinly to about 4/5" in diameter and you may have to roll/rotate the pan to achieve this.
When the batter is brown underneath and slightly bubbly on top, turn and cook on the other side (if you are feeling adventurous you could try tossing them). Best eaten when warm.