In a large bowl, mix together the butter and caster sugar.
Gradually add the flour and vanilla extract and mix until it forms a dough.
Wrap and chill in the fridge for 30 minutes.
Preheat the oven to 180 degrees Celsius or gas mark 4 and line a baking tray.
Roll out the biscuit dough to 0.5cm thick and cut out your desired shapes. For Valentine's biscuits, cut out a heart shape, and for every other biscuit, cut out a smaller heart shape inside (the window to the jam).
Bake for 20 minutes then leave to cool.
Spread the biscuit with jam and sandwich the two biscuits together. Dust with icing sugar to serve.