Method:

1) Preheat oven to 150°C.
2). Beat the butter and sugar together until creamy and pale: this will take 4-5 minutes with an electric beater.
3). In a seperate bowl, sift the plain flour, cornflour and salt together.
4). Now add the flour mixture to the butter, a tablespoonful at a time, only adding more when each is incorporated.
5). When it is all mixed in, bring together with your hands and divide soft dough into two balls.
6). Grease two 23cm springform pans.
7). With cold hands, press one ball of dough into each pan. Stop 0.5cm shy of the edge of the pan. (This way when the dough expands during cooking, it fills the tin and cooks evenly).
8). Prick all over with a fork and 'scallop' the edges by nicking round the edges with the fork. Lightly score each tin into 12 equal triangles.
9). If you have time, chill the tins in the fridge for 10 minutes.
10). Place in the preheated oven and bake for 40-45 minutes, until a pale golden brown.
11). Remove tins from the oven. Carefully cut each tin into 12 triangles and sprinkle over some sugar while still hot.
12). After allowing 10 minutes or so for the shortbread to firm up, carefully remove the shortbread slices from the tins.
12). Leave on a wire rack until cold. Store in an airtight container