For the jam:
For the biscuits:
For the filling
For the jam, put the raspberries in a small, deep-sided saucepan and crush them using a potato masher. Add the sugar and bring to the boil over a low heat. When the sugar is melted, increase the heat and boil for a further 4 minutes. Remove from the heat and carefully pour into a shallow container (pass it through a sieve if you'd rather not have seeds in your jam). Leave to cool and set.
For the biscuits, preheat the oven to 190C/170C Fan/Gas 5. Line 3 baking sheets with non-stick baking parchment. Using a 5cm/2in round cutter as a guide, draw 8 circles on each sheet of paper, spaced well apart. Turn the paper over so the pencil marks are underneath.
Measure the butter and icing sugar into a bowl and beat until pale and fluffy. Sift in the flour and cornflour and beat well, until thoroughly mixed. Spoon the mixture into a piping bag fitted with a medium star nozzle. Pipe 24 swirled rounds (not rosettes), inside the circles on the baking sheets.
Bake in the centre of the oven for 13—15 minutes, until a pale golden-brown. Cool on the baking sheets for 5 minutes then carefully transfer to a wire rack to cool completely and harden.
For the filling, measure the butter into a bowl and sift the icing sugar on top. Add the vanilla extract and beat with a wooden spoon or an electric whisk until very light and smooth. Spoon into a piping bag fitted with a large star nozzle.
Spoon a little jam onto the flat side of 12 of the biscuits and place jam-side up on a cooling rack. Pipe the buttercream over the jam and sandwich with the remaining biscuits. Dust with icing sugar to finish.