CupcakesPreheat oven to 350°F. Line muffin pan with baking cups.
In large bowl, beat yellow cake mix, eggs, water and peanut butter with electric mixer at low speed 30 seconds. Beat at medium speed 2 minutes. Fill baking cups 2/3 full with batter. Spoon 1 teaspoon jelly on top of batter in the center of each cup. Reserve remaining jelly for garnish.
Bake 18-20 minutes or until Cake Tester or toothpick inserted in center of cupcake comes out clean. Cool cupcakes in pan on cooling grid 5 minutes. Remove from pan; cool completely.
In large bowl, beat shortening and butter with electric mixer until creamy. Add peanut butter, and vanilla. Gradually add sugar, one cup at a time, beating well at medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry. Add milk, a tablespoon at a time, and beat at medium speed until light and fluffy.
Makes about 3 cups icing.
To Assemble: Ice cupcakes with Peanut Butter Buttercream Icing; if desired, decorate with tip 21 swirls. In microwave-safe bowl, microwave remaining jelly on High 10-15 seconds; stir until smooth. Drizzle over cupcakes and sprinkle with peanuts.