Preheat oven to 375 degrees Fahrenheit. Line a 13x9-inch baking dish with parchment paper (for lifting the bars out) or grease with cooking spray.

In the bowl of a stand mixer, stir together the flour, sugar, baking powder, and salt. Add the butter one Tablespoon at a time and mix with the paddle attachment until the ingredients resemble fine crumbs. Add the egg and mix until incorporated.

Press 2/3 of the mixture onto the bottom of the prepared baking dish. Bake at 375˚F for 10-12 minutes or until the crust is matte (not shiny/wet) and starting to lightly brown. 

While crust is baking, mix together the sweetened condensed milk, lemon zest, lemon juice, and egg yolks. Gently pour over the semi-cooked crust while still warm. Spread evenly with a spatula.

Crumble the remaining crust evenly over the top of the lemon filling. (Squeeze crumbs together in hands for bigger chunks.) Bake at 375˚F for an additional 20-25 minutes until the top is lightly brown and the filling is set in the center. 

Cool on a rack to room temperature. Then CHILL in the refrigerator for 2 hours or until cold. Lift bars out of the pan with the parchment paper. Cut and serve. Store leftovers in an airtight container in the refrigerator.