2) In a medium bowl, sift together the flour and salt; add them to the butter-sugar mixture. Mix on low speed until the dough starts to come together. Dump onto a surface dusted with flour and shape into a flat disk. Wrap in cling film and chill for 30 minutes.
3) Roll the dough 1cm thick and cut the biscuits with a 7.5cm heart-shaped cutter. Place the hearts on an ungreased baking tray and sprinkle with sugar.
4) Bake for 20 to 25 minutes, until the edges begin to brown. Allow the biscuits to cool to room temperature and serve.
Note: The edges of the shortbread will be slightly sharper if you chill the biscuits before baking them. I cut out the biscuits days ahead and bake them the day I serve them.