Preheat the oven to 180c / fan 160c and line the base of a 22cm spring form cake tin.

In a food processor whizz the flour, butter and sugar until you have a breadcrumb texture.

Tip the mixture into a bowl and mix in the chocolate pieces. Press half the mixture into the prepared tin, scatter over the raspberries and then the remaining shortbread mixture. Press the mixture down firmly and cook for 25 minutes until just golden.

Remove from the oven and sprinkle over the caster sugar. Score while warm and serve with vanilla ice cream when cool.