Shortbread: On a work surface shape the flour into a mound. Make a hole in the middle of the mound and add egg yolk, water, butter and icing sugar.
Using a knife combine all ingredients then when mixed knead by hand until smooth. Form a dough ball and transfer to a bowl. Cover and refrigerate for 10 minutes.
On a lightly floured surface cut the dough into 3 pieces and roll the dough out. Cut dough into desired shapes, making pairs. Arrange on a baking paper lined baking tray.
Refrigerate for 10 minutes. Meanwhile preheat oven to 180 degrees C.
Bake in middle of the oven for 10-15 minutes or until golden brown. Transfer to a rack to cool.
Filling: Spread redcurrant jelly onto one biscuit and stick on its corresponding pair. Repeat until you've sandwiched all biscuits together.
Icing: Mix together the icing sugar with 2 tablespoons redcurrant jelly. Brush the top of the biscuits from the inside to the outside