Preheat oven to 350 degrees. Line two 12-cup cupcake pans with cupcake liners and set aside.

In a medium mixing bowl, sift cake mix and flour and set aside. Beat together eggs, root beer, and root beer concentrate at low speed. Add cake mix and beat until just combined. Once all ingredients are incorporated, scrape the sides and bottom of the bowl and turn mixer up to medium and beat once more for 15–20 seconds. Do not overbeat.

Spoon three tablespoons of batter into each cupcake liner and bake on middle oven rack for 16–18 minutes, baking up to 24 cupcakes side by side at a time. (For best results, bake cupcakes one pan at a time.) Once a toothpick comes out clean, remove from oven and allow cupcakes to rest in pan for 2–4 minutes before removing and transfer- ring to a cooling rack. Prepare pan and repeat this step with any remaining batter.

While cupcakes are cooling, prepare frostings. To pre- pare root beer buttercream, cream butter at medium speed until soft and smooth. Add shortening and root beer concentrate and beat until combined. Slowly add in powdered sugar, beating slightly between each addition. Add small amounts of brown gel coloring and milk one tablespoon at a time, beating in between additions until desired consistency and color is achieved.Turn mixer up to medium-high and beat for 1–2 minutes.

For vanilla buttercream, in the bowl of a stand mixer (or large mixing bowl) using the paddle attachment, cream butter at medium speed until soft and smooth. Add shortening and vanilla extract and beat until combined. Slowly add in powdered sugar, beating slightly between each addition. Add milk one tablespoon at a time, beating in between additions until at desired consistency. Turn mixer up to medium-high and beat for 1–2 minutes.

Once cupcakes have completely cooled, frost cupcakes with the traditional swirl technique (page 24) combined with the two-toned effect (page 26) using a large circle tip.