Put the raspberries, jam and sherry in a medium bowl, mash to a paste with a fork, then stir well to ensure everything is evenly mixed.
Break the sponge fingers into small chunks, stir these through the raspberry mixture, then divide between six small glasses.
Put the mascarpone, cream and vanilla in a large bowl and whisk to soft peaks – err on the side of caution, because it will thicken further as it chills.
Spoon the cream on top of the raspberry mix in the glasses, then refrigerate for at least four hours.
To serve, crumble the shortbread into small pieces and scatter over the top.
