• Preheat oven to 350°F.

Mix and bake crust

• In a medium bowl or your stand mixer with the paddle attachment, cream 3/4 cup butter until light and fluffy. Add the 3/8 cup granulated sugar and beat until well blended. Add 1 1/2 cups all purpose flour and zest from one lemon and blend just until a crumb mixture forms.
  
• Press into the bottom of an ungreased parchment lined 9x9 inch pan. Bake shortbread for 20-25 minutes in the preheated oven, or until firm and golden. 
  

Make filling and bake

• While the crust is cooking, whisk together 1 1/2 cups granulated sugar and 1/4 cup all purpose flour in a separate bowl. Whisk in the 4 eggs and 2/3 cup fresh squeezed lemon juice. Pour over the baked crust.
  
• Bake for an additional 20-25 minutes. If adding sweetened dried lemon slices, press them into the top a few minutes before the baking is complete. Remove from oven and allow bars to cool to room temperature.
  

Chill and slice

• Transfer pan to the refrigerator and allow bars to chill. The bars will firm up as they cool.
• Once chilled, remove from pan. Optional: add powdered sugar for dusting.
  
• To serve, cut into nine 3-inch squares for large lemon bars or 16 smaller 2-inch squares.