Preheat the oven to 350 degrees. Line a 9x13 pan with parchment paper (for easier removal) or spray it with cooking spray.
For the crust, combine butter, flour, and powdered sugar until combined. You can use a food processor or mixer for this until it comes together. It may seem dry at first but it will come together. Press into the bottom of the pan and bake for 13-15 minutes.
For the filling, mix the sugar, baking powder, flour, eggs, lemon juice, and lemon zest until combined. Beat for 2-3 minutes. Poor over crust and bake for 23-25 minutes or until filling is set. Remove from oven and let cool. Sprinkle with powdered sugar for serving.
Store in the refrigerator. Before serving remove from fridge for about 10 minutes to let the crust soften. Makes about 20 bars.
Notes
Source: adapted Brittany's recipe. Added zest, more lemon juice, and more flour.