For the jam, put the raspberries in a small saucepan and crush them . Add the sugar and lemon zest 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.

Leave to cool and set.

For the biscuits, beat butter and icing sugar into a bowl 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 even swirled rounds on the a parchment paper lined baking sheets.

Place the biscuits for 30 minutes in the fridge.

Preheat oven to 375F (190C)

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, place the butter and icing sugar into a bowl. Add the vanilla extract and beat with a wooden spoon or an electric mixer 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.