Heat oven to 180 degrees C. Spray or grease a 22cm round, fluted tart tin.
Base: Melt butter and chocolate together until liquid. Whizz biscuits into crumbs then combine with melted butter and chocolate. Press this into the base and up the sides of the tart tin to form a lip. Put into the fridge to chill slightly.
Filling: Whisk together the cream, eggs, orange zest and orange curd then pour into the base.
Bake in the oven for 35 to 40 minutes until just set. Remove from the oven and leave to cool for about an hour.
Remove from the tin, drizzle with melted chocolate and leave to cool completely. Chill in the fridge before serving.
If your orange curd contains orange zest, you can leave this out.