Preheat oven to 350F. Spray a 13x9-inch pan with non-stick spray. Set aside.
In a large bowl, combine the flour, powdered sugar, and butter. Using your hands, mix until it comes together as a crumbly dough. Press into the prepared baking dish.
Bake for 20-25 minutes, until lightly golden brown around the edges. Remove from the oven.
Meanwhile, in an electric mixer fitted with a whisk attachment, mix together sugar, eggs, and lemon juice. Mix on medium speed for 4-5 minutes until light and fluffy, and the sugar is completely dissolved.
Add flour and baking powder, and mix until well incorporated.
Pour over the baked crust. Return to the oven and bake for 22-25 minutes.
Remove from the oven, and cool completely before dusting with powdered sugar, and serving.
Notes
To make the bars a little more tart, add the zest from the lemons into the filling.
Make sure to let the bars cool completely before cutting them or they won't hold their shape.
Store leftover lemon bars in an airtight container or bag on the counter for 2 days, in the fridge for 1 week, or in the freezer for 4 months.