Step 1

Preheat oven to 350 F degrees. Line an 8 x 8 inch baking pan with foil or parchment paper. Set aside.

Step 2

In a medium sized mixing bowl, combine the crust ingredients: melted butter, flour, powdered sugar, and cornstarch. Press the shortbread mixture into the prepared pan and spread evenly. Bake for 10 minutes and remove from oven.

Step 3

While the shortbread crust is baking, whisk together the filling ingredients: eggs, sugar, zest, lemon juice, flour, milk, and baking soda.

Step 4

Pour the filling onto the baked shortbread crust and bake for an additional 25 minutes or until the edges are light golden and the filling is almost set.

Step 5

Remove from oven and let cool completely at room temperature. Then cover with foil, and refrigerate for at least 2 hours or overnight.

Step 6

When ready to serve, slice the bars into squares, and dust with powdered sugar and garnish with lemon slices if desired.