Line an 8″ X 8″ square baking pan with parchment paper or foil. Preheat the oven to 350˚ F.
Combine all of the Shortbread Base ingredients in the bowl of a food processor, fitted with a blade. Pulse until it comes together into a ball of dough. Alternatively, use a mixer do by hand using a pastry blender.
Place the dough in the baking pan and flatten to evenly cover the bottom, working the dough quickly with your fingers. If the dough begins to get sticky, lightly flour your fingers and rework. If the dough becomes too soft to work with, place it all in the refrigerator for 10 minutes.
Dock the dough but punching it with the tines of a fork about 20 times. There will be a lot of fork holes all over the dough, which will keep it from bubbling up during baking.
Bake for 25 minutes, or just starting to firm on the edges, while you mix together the ingredients for the Shortbread Topping. Wrap the Shortbread Topping in plastic and place in the refrigerator.
Once the Shortbread Base has cooled, spread the lemon curd evenly across the top.
Remove the Shortbread Topping from the refrigerator and tear into pieces. Flatten the pieces with the heel of your hand on a workspace. Scrape up the pieces and lay on top of the lemon curd. It’s fine to overlap in places, and leave little openings to allow the curd to ooze through during baking.
Increase the oven temperature to 375˚ F, and bake for 25 – 30 minutes.
Cool slightly in the pan before removing. This is a very tender cookie bar, and will harden slightly during cooling, making it easy to handle.