1. Pre-heat oven to 180C for at least 15 minutes. Whisk sugar and flour together. Add the cold butter and rub it into the flour mixture with your fingertips. The mixture should resemble fine and crumbly sand.
2. Add egg yolk and gently mix it in with a rubber spatula until the mixture becomes a dough. This will take just a few seconds. Add the flaked almonds and knead the dough a little until the almonds are more or less evenly distributed.
3. Roll out the dough between two sheets of baking parchment until only about 1/8 inch thick and cut into 2 x 1 inch rectangles. Arrange the rectangles on a cookie tray lined with a sheet of baking parchment. Allow a slight gap between each piece. Bake on the centre rack for 25-30 min until golden brown. Cool on wire rack until complete cool and store in an airtight container.