Mix the melted butter and biscuits together until combined. Pour the mixture into a loose-base tart tin (approx. 10 x 35 cm) and press firmly along the bottom and up the sides. Cover and refrigerate the crust for at least 1 hour.
Melt the chocolate over a water bath and combine with the yoghurt. Pour the filling into the crust – using a piping bag if you have one. Decorate with raspberries and sifted icing sugar.
You can substitute dark or white chocolate for the milk chocolate.