Boil hot water in the bottom of a double boiler. Insert the top
of the double boiler and add egg yolk, granulated sugar and apple
cider. Beat the contents with a wire whisk or electric mixer until
thick and white.
top of the double boiler will heat up quickly, so beat swiftly to
prevent the egg yolk from hardening. If this is your first time
to make zabaglione, I recommend periodically removing the top of
the double boiler while beating the mixture.