makes 16-18
 250g very soft butter (not melted though)
50g icing sugar
250g plain flour
50g cornflour
1/2 tsp vanilla extract

Filling
100g very soft butter
200g icing sugar, plus 1/2 tsp for dusting
1/2 tsp pure vanilla extract
75g seedless red jam

Method
Preheat oven to 190C/ fan 170C. Line two baking tray's with greaseproof paper. 
Put the butter, icing sugar, plain flour, cornflour and vanilla extract in food processor and blitz until smooth.  you may need to remove the lid and push the mixture down a couple of times with a rubber spatula.  Alternatively, put everything in a large mixing bowl and beat with an electric mixer until smooth.
Spoon the dough into a piping bag fitted with a  large star nozzle.  Pipe 16- 18 circles or rosettes of dough on to the baking sheet, spacing them well apart. Each should measure about 6cm - about the size of a gingernut. Continue piping all the remaining mixture.
Bake the biscuits in the centre of the oven for 12-15 minutes or until they are pale golden brown and firm.  Transfer them to a wire rack.

To make filling, put the butter in a bowl and sift the icing sugar on top.  Add the vanilla extract and beat well until very light and smooth.
Put a little red jam in a small bowl and stir until smooth.

To assemble, spoon a little jam on to the flat side of half of the biscuits and place them jam-side up on the wire rack.  Gently spread the butter cream icing on to the remaining biscuits and place on the jam-topped ones to make biscuits sandwiches.  Put the biscuits on a serving plate and dust with icing sugar before serving.