Preheat oven to 350F/180C.

Cream the butter and sugar - can use hand blender or a 'proper' mixer, both will work.

Add flour and corn starch/cornflour and mix together but be careful not to overmix.

Roll out mixture on a surface floured with a little corn starch to around ¼ inch/3-4mm thick. Don't worry that it will probably crack,just put to one side and add to leftovers after cutting.

Cut into squares or rectangles around 1 ¼ - 1 ½ inch/3 - 4cm across. Press together the leftover pieces, roll out again and cut more squares/rectangles until all of the mixture is used up.

Spoon a little jam on top of one square/rectangle - around ½ teaspoon for the suggested size - and put another square/rectangle on top and press edges together. It's easiest to do this by gently pressing with the side of a knife (see picture above).

Place shortbread on a baking tray and bake for approx 10 minutes until lightly golden.

Remove onto a cooling rack while still warm, or at least ensure loosened on tray. You can sprinkle with sugar while still warm if you like.