Combine shortening and peanut butter in a medium mixing bowl, stirring well. Gradually add sugar, beating until light and fluffy. Add egg, and beat until well blended.
Combine flour, baking powder, and salt in a small mixing bowl; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Stir well after each addition.
Spoon batter into greased muffin pans, filling two-thirds full. Bake at 350° for 20 minutes or until lightly browned. Cool slightly in pans; remove from pans, and serve warm with jelly, if desired.