In a medium bowl, combine flour, brown sugar, and butter.
Using a pastry cutter or two forks, cut in the cold butter until the mixture is crumbly.
Press into bottom of 9x13 pan.
Bake the crust at 350 for about 20 minutes.
In separate bowl whisk eggs.
Add lemon juice ,zest, and vanilla.
Then slowly whisk in powdered sugar until dissolved.
Pour over hot baked crust.
Bake at 350 for about 30 minutes until filling is set
Let cool and refrigerate for at least 2 hours before cutting.