Put the butter and sugar into a bowl and mix well with a wooden spoon or electric mixer.Then slowly beat in the egg yolk and lemon juice.Sift the flour and a pinch of salt into the mixture, add the lemon zest until thoroughly combine.
Bring the mixture together to form a smooth ball, split the ball into two and cling film the two balls. Then place in the fridge to chill for 30 minutes.
Preheat the over to 190°C/375°F/Gas mark 5.Line two baking trays with baking parchment .
Unwrap the dough and roll out to the thickness of a one pound coin.After, use a circular cutter (I use 6 cm circle cutters but you can do them any shape) to cut out circles from the sheet.
Bake for 10-15 minutes, until golden brown.Leave to cool for 5-10 minutes, for them to cool quicker put on a cooling rack.
For the icing, mix together the egg white and lemon juice .Gradually whisk in the icing sugar until smooth. Ice the biscuits with a piping bag and then add the preferred topping e.g chopped fruit peel or edible gold/sparkle spray.