Preheat oven to 350°F (177°C). Line a 9x13 inch baking pan with parchment paper, leaving some overhang on the sides to lift the bars out later.
Make the crust: In a medium bowl, mix the melted butter, 2 cups flour, and ½ cup sugar until a soft dough forms. Press evenly into the prepared baking pan.
Bake for 15 minutes.
Make the filling: In a large bowl, whisk the eggs and 1 ½ cups sugar together until combined. Whisk in the ¼ cup flour, lemon juice, and lemon zest.
Pour the filling over the warm crust. Bake for 20 more minutes, until the center is almost set.
Allow to cool completely in the pan set on a wire rack. Lift the bars out using the parchment paper overhang and cut into squares.
