Whisk together butter and sugars, stir in the egg, root beer and extract. Add your flour and salt and beat until smooth.
Pour batter into a cup filling just past the half way point.
Microwave for 1-1/2 to 2-1/2 minutes, until the cake rises and is firm. Allow them to cool
Notes
If you don't have self rising flour just whisk together 1 Cup of All Purpose Flour, 3/4 tsp. baking powder and a little salt... thats all now you are ready!