Preheat oven to 350 degrees F. Grease 9x13-inch baking dish.
In medium bowl, stir together shortbread crust ingredients. Press firmly into baking dish.
Bake uncovered 20 minutes.
In clean medium bowl using a hand-mixer, beat together 4 eggs, sugar, and flour until fully combined. Add in lemon juice and vanilla extract. Mix well.
Pour lemon mixture over the baked crust while it is still warm.
Return lemon bars to oven and bake uncovered 30 minutes.
Remove lemon bars from oven. Cool 10 minutes then sprinkle liberally with sifted powdered sugar.
Cool completely. Refrigerate until ready to serve.