Before starting, make sure to set out butter to soften, and egg to warm to room temperature. 

In a small bowl, combine flour, baking powder, and salt. Set aside. 

In a separate bowl, cream together butter and sugar. Preferably at least 2 minutes. Add egg and vanilla. Mix until thoroughly combined and creamy. 

Alternately add flour and milk. Based on Beth's original recipe, this scaled down version should require 4 tbsp milk plus 1 tbsp. However, I reduced the flour by a tablespoon as well. That being said, all flours absorb differently, so I'd add it one tablespoon at a time. 

Allow batter to rest for 20 minutes, and meanwhile, preheat oven to 375*. 

Portion batter into 6 (7 is probably better) paper-lined muffin wells. 

Bake for 18-20 minutes. I'd check on them at 15 minutes, just in case your oven runs hot. 

Allow to cool completely, then frost with your favorite frosting. Pillsbury and Duncan Hines canned frostings are both marked gluten free.