Heat oven to 350ºF. If not using silicone pans, lightly coat two 6-cup muffin tins with vegetable cooking spray.
In a large bowl, with an electric mixer on medium-high speed, beat the butter and brown sugar until light and fluffy. Reduce speed to slow, add the remaining ingredients, and beat for 3 minutes or just until smooth.
Spoon the batter into the muffin pans. Bake 25 to 30 minutes or until a toothpick inserted into a muffin comes out clean. Remove from oven and cool on a wire rack.