Chocolate Chip Whoopies

1. Cut butter into small chunks and place in a saucepan. Heat over medium heat until completely melted, and continue to stir until butter becomes somewhat clear and brown-ish colored (about 5–8 minutes.)
2. Remove from heat and add to the sugars (do not stir or mix together) and allow to come to room temperature. Put in the fridge for about 10 minutes.
3. Meanwhile, prepare dry ingredients. In a separate bowl, sift together flour, cake flour, baking powder, baking soda, and salt.
4. Once sugar/butter mixture is completely cooled, beat together until fluffy. Add eggs, egg yolk and vanilla.
5. Add the flour mixture to the butter and sugar mixture, one cup at a time, until just combined.
6. Once all ingredients are combined, mix in chocolate chips. Place dough in fridge for about 20 minutes to chill. Meanwhile, preheat oven to 350ºF.
7. Once dough is chilled and oven is ready, spoon dough into desired size and roll together in your hands to ensure uniform size and baking shape. (This is important!)
8. Bake cookies on a parchment paper-lined cookie sheet for approximately 12 minutes, until holes/cracks appear in the middle of the cookie and the border becomes golden brown.
9. Let cookies cool completely for one hour before assembling whoopies.
11. While waiting, prepare your frosting.
10. Once cookies are completely cooled, match each one with the one that most closely resembles its size and shape. Flip one of each of the pairs so that the flat edge is facing up.
11. Fill a pastry bag with frosting, using the star attachment. Holding the bag at a 45 degree angle and about 1/2″ away from the cookie, outline the outer edge of the flipped cookie and complete the outline. Fill in the rest of the cookie with circles with decreasing size until cookie is completely frosted.
12. Gently place the other half of the whoopie on top of the frosted half and repeat until all cookies are matched.