Preheat the oven to 350F/180C degrees.
Line 12 standard cupcake pan wells with cupcake liners.
In a small saucepan, heat the Coca-Cola, cocoa powder, and butter over medium heat until the butter is melted. Add the granulated and brown sugars and whisk until dissolved. Remove the mixture from the heat source and let cool for about 10 minutes.
While the Coca-Cola mixture cools, in a medium bowl whisk the flour, baking soda and salt together.
In a small bowl, whisk the egg until foamy, then whisk into the cooled cocoa mixture. Getnly stir the flour mixture into the cocoa mixture. It will be thin and might be a little lumpy, that is fine.
Divide the batter evenly among the cupcake liners (note: Since the batter is thin, it might help to pour it into a bowl with a pour spout to help better control your pouring.), fill the liners a generous three-quarters full. Bake the cupcakes for 18-20 minutes, or until the cakes spring back when pressed in the middle.
Transfer to a cooling rack and allow the cupcakes to cool completely before frosting.