Put the raisins and Marsala in a saucepan and bring to the boil. Turn the heat off and leave to cool.
Line a 20cm cake tin with baking parchment (cut to 30cm diameter) and fold the edges as you go round. Do not cut it as you need to keep all the moisture inside as it cooks.
Mix the biscuit crumbs with melted butter and press into the bottom of the tin