Pulse until the mixture reaches a fine crumble consistency
You want the butter to be well combined but to stop before the mixture turns into a ball (alternately you can combine the crust ingredients together in a mixing bowl with a pastry cutter or a fork)
Sprinkle the crust mixture evenly into the prepared pan
Then press the mixture down firmly to form an even layer
Bake the crust for 20 minutes or until it is lightly golden on top
Meanwhile whisk the lemon filling ingredients together in a medium mixing bowl until combined.
If your powdered sugar or flour are too chunky or there are lots of bubbles whisked into the filling feel free to just pour the filling through a fine-mesh strainer to get it nice and smooth before adding it to the crust (but if there are a few little clumps that’s ok too!)
Once the crust is done baking remove the pan from the oven and immediately pour the lemon filling on top of the hot crust
Return the pan to the oven and bake for 18-20 more minutes, or until the lemon filling has set
Remove the pan from the oven and transfer to a wire baking rack to cool until the bars reach room temperature
Then transfer to the refrigerator and let the bars chill for at least 2 hours
Sprinkle the tops of the bars with extra powdered sugar if you would like, then slice and serve