Sieve the flour into a large mixing bowl and rub in the butter (preferably room temperature) with your fingers until the mixture resembles fine breadcrumbs.
Stir in the caster sugar and vanilla extract and bring the mixture together with your hands to make a firm dough.
On a lightly floured surface, roll out the dough to a thickness of 2.5cm/1in. Stamp out about as many hearts shaped biscuit cutter (or any other shape!) as you can.
Arrange the hearts on a lightly greased baking tray (cookie sheet), with good space in between them. I used two trays to accommodate 17 biscuits. Bake in a preheated oven, 180C/350F/Gas Mark 4 for 15-20 minutes until the hearts are a light golden colour.
Transfer the vanilla biscuits to a wire rack and leave to cool. You can sprinkle a bit of caster sugar on them.