Preheat the oven to 350 F.
Line a 8×8 inch baking pan with parchment paper. Spray the parchment paper with baking spray (or grease with butter). In a medium bowl, beat the butter and the sugar until fluffy. Beat in the flour until a soft dough is formed.
Remove the dough and place it into your prepared pan. Press firmly onto the bottom and sides of the pan.
Bake for about 15 minutes or until golden brown.
In a small bowl, whisk the whole eggs sugar and flour. When it is smooth, add in the lemon zest and the juice. Whisk together until incorporated. Taste the filling, if you would like it more tart, add a little bit more of the fresh lemon juice. *5 Tablespoons is enough for my taste, but you may like it more tart.
When crust is ready, remove from the oven and lower the temperature to 300 degrees.
Spoon the filling over the crust and smooth over with a spatula.
Return pan to oven and bake until the filling is just set, about 30 to 35 minutes.
Lift the cooled bars out of the pan, using the parchment paper as handles. Let cool on a rack to room temperature.
Cover and place in the refrigerator until cold (or overnight). Bars are better sliced when cold.
Slice the bars into squares (I cut them into 12 small squares) and dust with confectioners’ sugar just before serving. The crust will soften over time. Store for a few days in the fridge.