For Shortbread Crust

Preheat oven to 350 degrees. Line a 8 x 8 baking pan with parchment paper, allowing the paper to hang over all four sides by about 2 inches for easy removal of the bars once chilled

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar until light and fluffy. About 2 minutes.

Combine the flour and salt in a medium bowl and add to the butter mixture while mixing on low. Mix until just combined. Transfer the dough onto a well-floured surface and gather into a ball. Gently flatten the dough with lightly floured hands and press it into the prepared pan. Use your fingers to press the dough up the sides of the pan about 1/2 inch. Chill the dough for 30 minutes.

Bake the crust on the center rack of the oven for 15 to 20 minutes. The crust should be lightly browned at the edges. Do not over bake. Remove from the oven and cool on a wire rack while you make the lemon filling. If the crust has puffed up, use the back of a measuring cup or a flat spatula to gently press the crust down evenly. This will help it to hold together well once sliced.

Lower the oven temperature to 325 degrees.

For Lemon Filling

Place the lemon zest and softened butter in a large bowl. Set aside.

In a medium saucepan, whisk together the sugar, eggs, egg yolks and salt to combine well. Slowly add the lemon juice. Continue stirring constantly over medium low heat until the mixture begins to thicken. For best results, use an instant read thermometer and cook the filling until it reaches 160-165 degrees. As it cooks, use a silicone spatula to scrape the sides and bottom of the pan to prevent the filling from burning. Lower the heat as it continues to thicken so as not to curdle the eggs. The filling should coat the back of the spatula. If the mixture begins to bubble or the eggs become lumpy, remove from the heat immediately.

Once the filling has reached the desired temperature and consistency, remove the pan from the heat and strain it over the bowl with the butter and lemon zest. Use a spatula to stir the mixture until all of the butter is melted and the filling is smooth and shiny.

Pour the filling over the cooled crust and return the pan to the oven. *Make sure the oven temperature was reduced to 325 degrees.

Bake for 15-20 minutes. The center of the bars should resemble jello and still have a slight jiggle when shaken. The bars should not be runny or look under baked. The filling will set as it cools.

Remove the pan from the oven and cool on a wire rack for one hour before placing in the refrigerator for 3 hours or overnight.

Use the parchment overhang to remove the bars from the pan once chilled. Slice into bars and dust with confectioner’s sugar before serving.