Line the tin with cases, and line a small tray with parchment paper.
Melt the butter in a large saucepan over a low heat.
Blitz the biscuits and 2 tbsp of the pistachios in a food processor, or seal in a food bag and bash with a rolling pin, until you have fine crumbs and finely crushed nuts.
Stir into the melted butter to coat well, and divide evenly between the cases.
Press the crumbs firmly into the base and up the sides, cover with cling film and chill for about 1 hour, until set firm.
About 15 minutes before the cases are ready, prepare the filling. Snap the chocolate into a medium heatproof bowl and add the cream.
Either melt the chocolate in the microwave in 30-second blasts, stirring between each go, or over a pan of simmering water, shallow enough that the water doesn’t touch the bowl.
Once melted, stir until smooth and add the vanilla seeds. Leave to cool to body temperature.
Use the tip of a pointed knife to lift the tarts carefully out of the tin. Gently peel the paper cases away and arrange on the tray. Spoon the filling equally between them and chill for 15 minutes or until the filling is set. These can be prepared a day in advance.
When ready to serve, arrange on a pretty tiered cake stand. Sit a raspberry, pointy side up in the centre of each one. Roughly chop the remaining tablespoon of pistachios and scatter over.