Preheat oven to 375 degrees F.
Grease 9x13" pan with cooking spray and set aside.
In large bowl, beat butter and sugar until light and fluffy, about 2 minutes.
Add eggs, one at a time, beating well to combine.
Add vanilla extract and lemon zest, beating well.
In medium bowl whisk together flour, salt, and baking soda.
Add slowly to butter mixture and beat until combined.
Pour into prepared baking dish and spread out evenly.
Bake in preheated oven 15-20 minutes. The bars will be barely set and will not have any color around the edges...that is okay!
Let cool completely.