While the shortbread base is baking, make the top layer.
In a large bowl, whisk together the sugar and cornstarch to remove any lumps.
Then whisk in the eggs, followed by the cooled ¼ cup of reduced raspberry puree.
Carefully, whisk in the lemon juice. The mixture will be quite liquidy.
Pour the lemon raspberry mixture over the baked shortbread base.
Bake in the oven (stillat 325F/160C) for 20-25 minutes, or until the top looks set.
Remove from the oven. Cool the bars in the pan for at least 1 hour or until room temperature. Then cover the pan and place in the fridge to chill for at least 2 hours.
When ready to slice, lift the bars out of the pan using the overhang of the parchment paper from the long sides of the pan.
Place the bars on a cutting board and slice with a sharp knife. For clean cuts, whipe off the knife after each cut. Store bars in the fridge.