Sift the flour, cocoa and baking soda into a large bowl; set aside. In a small saucepan, cook peanut butter and oil over low heat for 2-3 minutes or until peanut butter is melted. Remove from the heat; stir in sugar and sugar blend until smooth. Stir in the milk, vinegar and vanilla. Pour into flour mixture; stir until blended.
Fill paper-lined muffin cups half full. Bake at 350° for 15-20 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.
For frosting, in a large bowl, beat peanut butter and butter until light and fluffy. Beat in the confectioners' sugar, cocoa, milk, vanilla and salt. Frost cupcakes. Sprinkle with jimmies if desired.
Editor’s Note: This recipe was tested with Land O'Lakes light stick butter and Splenda sugar blend.