Line conventional size cupcake pan with paper liners. Mix cake according to manufacturer’s instructions then use a #16 blue scoop to deposit 1.5oz batter into each cavity. Bake at 350F until cupcakes spring back lightly when touched. Let cool completely. Mix together tequila flavoring and key lime filling to desired taste, reserve. Mix together 5 pounds buttercreme, 1oz lime juice, and 0.5oz tequila flavoring, reserve. Using a very small round cutter, cut the center out of each cupcake. Fill the cavity with prepared lime filling. Place buttercream in piping bag fitted with a closed star tip and pipe a rosette on the top of each cupcake. Roll the edges in sanding sugar (to look like the rim of a margarita glass) and top with a slice of lime.