Preheat the oven to 180C/170C Fan/Gas 4. Grease two baking trays and line with parchment.
Cream the butter and sugar together in a bowl until pale and fluffy. Gradually sift and fold in the flour, cornflour and salt gradually until it binds together. Tip on to a lightly floured work surface. Knead together (take care not to overwork it). Wrap in cling film and put in the fridge for 15 minutes.
Meanwhile for the jam, put the raspberries and sugar in a heavy-bottomed pan and bring to the boil. Add the lemon zest and continue to boil for 5 minutes, see the tip section for how to check if the jam has set. Strain into a glass bowl, cover with cling film and put in the fridge.
Flour a work surface and roll the dough to 6mm/¼in thick. Use a small cookie cutter to cut 48 circles. Use an apple corer to cut out a small circle in the centre of 24 of the biscuits. Place on the prepared baking trays. Bake for 15 minutes, or until the edges are just starting to brown. Leave to cool on the baking tray for 10 minutes before carefully moving to a wire rack.
For the buttercream, cream the butter in an electric mixer until light and fluffy. Add the icing sugar, cream and vanilla extract and mix well. Place in a small piping bag.
Mix the royal icing sugar with a little water until a smooth mixture is achieved. Place in a piping bag.
To assemble, put a dollop of jam on a shortbread disc. Pipe the buttercream around the jam. Place a disc with the centre cut out on top and gently push down. Pipe a smile and eyes with the royal icing. Repeat this process with the remaining shortbread, buttercream, jam and royal icing to make 24 sandwiches.