Sift the flour into a mixing bowl. Add the butter and rub in until the mixture resembles fine breadcrumbs.Stir in the caster sugar.
Make a well in the centre and drop in the egg yolk. Add the vanilla extract and a teaspoon of water. Bring the mixture together with your hands to form a soft dough, adding a little more water if required. Cover and chill for 30 minutes.
Roll out the dough on a lightly floured work surface to about 5mm thick. Using a cookie cutter cut out as many hearts as you can and place on a lightly greased baking sheet. You will need two baking sheets for all the biscuits.
Gather the trimming together and re-roll and continue to cut our more hearts until all the dough has been used. Chill for a further 20 minutes.
Preheat the oven to 190℃ /170℃ fan/gas mark 5. Bake for 10–12 minutes until pale golden swapping the baking sheets around for the last few minutes.
Allow to cool on the baking sheet for a few minutes then transfer to a wire rack to cool completely.
To decorate the biscuits
Sift the icing sugar into a small bowl and beat in enough water to make a smooth thick icing.
Divide between two bowls and colour one bowl of icing dark pink and the other a pale pink.
Thin the icing to flooding consistency (see blog).
Spoon into two piping bags fitted with a plain nozzle.
Pipe the outline of one heart with dark pink then flood the centre to fill.
Pipe small dots around the edge of the hearts , then use a skewer to drag through the dots.
Repeat until you have iced half the biscuits then reverse the colours for the second half.
Allow to dry before serving.
Nutrition information is calculated usingan online nutrition database - is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)