Pre heat your oven to 180C/160C fan/gas 4 and line 2 baking trays with baking paper.
Add your butter and sugar to a large bowl and whisk until fully combined and pale in colour.
Combine your flour, baking powder and cornflour together in a separate bowl and fold into your buttercream mix slowly making sure it’s all combined. Your biscuit mix will have a tacky and sticky texture.
Add your biscuit mix to a piping bag and pipe 2 inch circles on the mic (a star nozzle will give you that classic finish here).
Pop you trays in the oven for 12mins (keep an eye they should be a lightly golden finish). Leave to cool on a rack.
Add your softened butter, sugar and vanilla to a bowl and beat until pale and the beaters leave a trail, pop in the fridge before adding to your piping bag.
Lay all of your biscuits out flat side up and split into 2 batches. Pipe your cream onto 1 batch (flat side) then add a teaspoon of jam on top. Finish by adding your second batch of biscuits on top of each biscuit to create a sandwich, add a dust of icing sugar and enjoy.