Work all the biscuit ingredients into a smooth dough. Wrap and chill for 2 hours.
Preheat oven to 200 C / Gas 6. Grease baking trays.
Roll dough out to 5mm thickness and cut out heart shapes. Transfer to baking trays and bake for 15 minutes or until golden brown. Allow to cool.
Stir half of the icing sugar with the lemon juice until smooth, until you have a thick icing. Spread the icing over half of the hearts. Mix the remaining icing sugar with syrup and coat the other side of the hearts with it. Allow the icing to set.