Lightly grease two baking trays.
Sift the flour into a bowl.
Make a well in the centre and add the sugar, butter and egg yolks.
Using your fingertips, blend the butter and egg yolks into the dry ingredients.
Knead the mixture lightly to form a soft dough.
Wrap the dough in cling film and chill for 30 minutes, or longer if you have time.
Roll the dough out on a lightly floured board to a 23 cm/9 in square.
Cut it into smaller squares of 3.5cm/1 1/2 in.
Using a palette knife, carefully transfer the biscuits to the prepared baking trays.
Bake the biscuits in a moderate oven (180C, 350F, gas 4) for about 18 minutes, or until golden brown.
Remove the hot biscuits from the trays and transfer them to a wire rack to cool completely.
While the biscuits are cooling, make the filling.
Cream the butter until very soft, light and fluffy.
Make a syrup with the icing sugar and milk and beat this into the butter, together with the coffee essence and chocolate.
Sandwich the biscuits together in pairs with the filling.
Make the coffee glace icing according to the recipe instructions.
Place a small dab of icing on top of each biscuit and decorate with a coffee bean.