Step 1

Place caster sugar, butter and 220g raspberries in a saucepan over medium-low heat. Bring to a simmer, and cook, stirring, for 5-6 minutes until reduced by one-third. Add the cornflour, and cook, stirring, for a further 2 minutes or until slightly thickened. Remove from heat and set aside to cool slightly, then fold through the remaining 80g raspberries. Set mixture aside to cool completely.

Step 2

For the pastry, combine the frozen butter, flour and icing sugar in a food processor and whiz until a crumb forms. With the motor running, add 2 tbs cold water, a few drops at a time, until a soft dough forms. Turn dough out onto a lightly floured work surface and lightly knead with your fingertips until smooth and soft, then shape into a disc and enclose in plastic wrap. Chill for 30 minutes.

Step 3

Preheat oven to 180°C and grease a 23cm pie pan. Set aside one-third of the dough. Roll out remaining dough into a disc 4mm thick, then use to line tart pan. Roll out reserved one-third of the dough to 4mm thick, then cut into long, thin strips. Spread the raspberry filling in the tart shell, then top with pastry strips in a criss-cross pattern. Using a fork, gently press the strips against the shell to join. Trim the edges of the pastry so there is no overhang. Sprinkle tart with extra 1 tsp caster sugar and bake for 35-40 minutes until golden. Remove from oven and cool in the pan for 5 minutes before serving.