In a large mixing bowl, mix the flour, sugar and butter together on low speed until crumbly. Press into the bottom of a 13×9 dish and bake at 350 degrees for 20 minutes, until golden brown around the edges.
While the crust bakes, mix together the lemon juice, lemon zest, 2 c. sugar, eggs, flour, baking powder and salt until fully mixed and frothy.
Pour the lemon mixture over the hot crust and bake at 350 degrees for 20-25 minutes, until top is lightly browned.
For glaze: whisk together powdered sugar and vanilla. Slowly add lemon juice until desired consistency. Drizzle glaze over cooled lemon bars.