Preheat your oven to 350 degrees Fahrenheit and grease some muffin pans.
In a large mixing bowl, combine the first 10 ingredients.
In a separate bowl, cream the butter and brown sugar. Then add in vanilla and buttermilk and mix well. Afterward, add the eggs and continue mixing.
Fill the prepared muffin pans with the batter (about 3/4 full). Then bake the batter in the oven for 20 minutes. Once the muffins are ready, take them out of the oven to cool.
Spread the frosting over the muffins. Once you're done, serve and enjoy.