Line a quarter sheet pan with parchment paper, and set aside.
Turn oven on 375 fahrenheit
Cookie Bar Directions
In one bowl, mix flours, baking powder, cream of tartar, and salt together.
In a seprate bowl attached to the stand mixer, combine butter, sugar, and shortening and beat on medium high until light and fluffy.
Add eggs to butter mixutre, and beat until mixed in, apx 45 seconds.
Next, add the vanilla, lemon zest, and extracts to the butter mixture. Scrape everything down with your spatula, and beat until incorperated.
Turn off mixer, and slowly add flour mixture into the butter mixture. Beat slowly for a few seconds, and gradually raise mixer speed to medium high. Mix everything unti just combined, about a minute.
Plop dough out onto prepared sheet.
Cook for 15 minutes, or until the edges start to turn light brown. Let cool before frosting.
Frosting Directions
Combine butter, sugar, and vanilla. Beat on low speed, and gradually increase mixer speed. Beat until fluffy.
Add vanilla and pinch of salt.
Gradually add water and beat until mixed.
Assembly
Once the bars have cooled, spread frosting on top.