Start with the cookie base. Combine the butter, sugar, and flour in a large bowl and mix until you have a firm dough. Line your baking pan with parchment paper and spread the dough as a even layer on the bottom of the prepared pan. Press firmly.

Bake for 25 minutes at 180°C/350°F (convention oven) until golden brown.

While the shortbread base is in the oven, you can start making the lemon layer right away. Put all the ingredients -sugar, flour, whole eggs, lemon juice and lemon zest- in a medium bowl and whisk until the sugar is dissolved. Let the mixture stand until the cake is ready.

Remove the golden brown cookie layer from the oven and pour the lemon mixture over it. Put your baking pan back in the oven.

Bake the lemon bars at 180°C/350°F for 20-25 minutes. The lemon layer should be firm but not rock hard. It's okay if it's a bit jiggly right out of the oven. It will set when it cools.

Allow the lemon bars to cool completely before cutting them into bars with a sharp knife. Sprinkle some powdered sugar on top of the bars before serving, it makes them look so pretty.