Preheat the oven to 175 degC. Line 3 cupcakes pans with cupcake liners. Combine the flour, 1 3/4 cups of the sugar, baking powder, and salt in a large mixing bowl and whisk to combine.
Add the butter, lime zest, and 1 cup of the buttermilk. With an electric mixer, beat on low until combined, and then raise the speed to medium, beating for 2 more minutes until the batter is light and airy.
In a medium bowl, combine the egg whites with the remaining 1/4 cup buttermilk, and whisk thoroughly. Add the egg white mixture to the batter in 3 additions, scraping down the sides of the bowl with each addition, beating only enough to mix evenly. Spoon the batter into each cupcake liner, so that the liner is approximately 2/3 full.
Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool.
While the cupcakes are cooling, make the Cachaça-lime syrup. In a non-reactive small saucepan, combine the remaining 1/4 cup sugar and the lime juice with the Cachaça. Bring the mixture to a boil, stirring to dissolve the sugar. Careful this will get very hot and may splash a little. Remove from heat, and brush the top of the cooled cupcakes with the syrup, and allow to cool completely before frosting.
For the icing:
In a large mixing bowl, beat the butter until light and fluffy, about 2 minutes. Gradually add the confectioners’ sugar, 1 cup at a time, and beat until smooth after each addition. Add the lime juice, zest and Cachaça and beat until light and fluffy, about 3-4 minutes. Frost the cupcakes with a piping bag and tip of your choice. To turn these into “World Cupcakes”, top each cupcake with a flag representing a team in the World Cup. Cupcakes will keep for 3 days at room temperature, kept in an air-tight container.