I N G R E D I E N T S
In the bowl of an electric stand mixer, fitted with a paddle attachment, cream butter and brown sugar on medium speed. Cream until slightly pale and fluffy, about 3 minutes.
Stop mixer, scrape down the bowl with a spatula, and add egg and vanilla extract. Beat for 1 minute.
Turn the mixer off, scrape the bowl, and add the dry ingredients. Beat on low speed while adding the sour cream. Beat until the batter just comes together. Batter will be pretty thick. Remove the bowl from the mixer and finish incorporating ingredients with a spatula.