First weigh the egg in the shell and record the weight. Measure the same weight of butter, and twice the weight of sugar.
Melt the butter in a non-stick pan; add the sugar and lemon juice. Stir over medium heat until the sugar is dissolved; allow to cool.
Beat the egg lightly and add to the pan, then put back over a medium heat. Slowly bring to near boiling point, stirring continuously. Pour into decorative jam or marmalade pots and store in the fridge.