Preheat the oven to 350℉.
Line a standard cupcake pan with liners. Set aside.
In a medium sized bowl, combine the flour, baking soda, baking powder, and salt. Stir and set aside.
In a standing mixer with the paddle attachment,( OR a hand mixer with a large bowl) add the butter, oil, and sugar. Beat until the mix is light and fluffy. About 2 minutes.
Add the root beer extract. Beat for 1 minute.
Add the egg and beat until combined. Next goes the sour cream. Beat again until combined.
Not add 1/4 of the flour and mix, then goes half of the milk. Beat.
Now add more of the flour, mix and the remaining milk. Finish with the last of the flour. Beat until combined.
Pour the batter into the cupcake liners. About 2/3 full.
Bake for 18 minutes or until a toothpick comes out clean.
Let them cool and move on to the frosting.