15 eggs, room temperature
1 cup milk
1 1/2 teaspoons baking powder
1 teaspoon lemon zest
3 cups all-purpose flour
1 teaspoon baking soda
4 teaspoons baking powder
1 teaspoon salt
2 cups semisweet chocolate chips
Beat together eggs and milk, beat in vanilla extract. Beat 3 additions by hand, giving each a little turn, until blended. Cover and refrigerate 25 minutes.
Preheat oven to 350 degrees F (175 degrees C).
In a large bowl, stir together flour, baking powder, lemon zest, and sugar until just blended. Mix together the flour mixture, baking soda, baking powder mixture, and salt; stir into the egg mixture just until blended. Spread the mixture evenly into the bottom and sides of a 9x13 inch baking pan. Cover the dough with remaining plastic wrap.
Bake in preheated oven for 25 minutes. Reduce heat to 350 degrees F (175 degrees C) and continue baking 20 minutes more, until crust is golden brown. Once cool, shape with a fork and sprinkle with chocolate chips. Allow to cool completely.