In a stand mixer with the paddle attachment, beat together the butter, sugar, flour, and salt until the mixture comes together. The mixture will be crumbly.
Press the shortbread in an even layer into the prepared pan. Use a fork to make a few holes in the crust. Blind bake the crust for 20 minutes.
While the crust bakes, make the lemon layer. Sift the sugar and flour together in a large bowl to get rid of any clumps. In a separate bowl mix together the eggs, lemon juice, and lemon zest. Add to the flour and sugar mixture and whisk until just combined. The mixture will be thin.
Take the crust out of the oven and pour the lemon layer over the blind baked shortbread crust.
Lower the oven temperature to 325°F and bake for 20-25 more minutes or until the center no longer jiggles. Take the bars out of the oven and allow to cool completely.
Once the bars are completely cool, transfer to the fridge to set for 2 hours (or overnight) until ready to serve! Slice the lemon bars and serve cold with a dusting of powdered sugar!