For cupcakes: Mix flour, baking powder, salt and cinnamon. In a separate bowl mix butter, peanut butter and brown sugar until blended. Add vanilla and egg. Add milk and flour mixture alternately while still mixing. Pour into lined cupcake pan and bake at 350* for 20 minutes, or until toothpick comes out almost clean.
For Ganache: Melt chocolate and cream in metal bowl set in simmering water.
For Frosting: Beat peanut butter and vanilla until blended. Add 3 tbsp milk and sugar while beating. Add the rest of the milk and sugar and beat until smooth. If needed, add a couple more tbsp milk.