1. Preheat oven to 375°.
2. To prepare the cookies, weigh or lightly spoon flour into dry measuring cups, and level with a knife. Combine flour, baking powder, and salt, stirring well with a whisk. Combine granulated sugar, 1/4 cup peanut butter, and butter in a large bowl; beat with a mixer at medium speed until well blended (about 2 minutes). Beat in milk. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla. Add flour mixture to sugar mixture; beat at low speed until well blended.
3. Spoon dough mixture into a pastry bag fitted with 1/2-inch round tip. Pipe 36 (1 1/2-inch-round) mounds onto 2 baking sheets coated with cooking spray. Bake at 375° for 11 minutes. Cool 1 minute on pans. Remove from pans; cool completely on wire racks.
4. To prepare the icing, combine 3/4 cup powdered sugar, 2 tablespoons milk, 1 tablespoon cream, and 3 tablespoons peanut butter in a medium bowl; stir well. Spoon peanut butter mixture into a small zip-top plastic bag; set aside. Place chips in a medium glass bowl, and microwave at HIGH 30 seconds or until almost melted, stirring until smooth. Add the remaining 3/4 cup powdered sugar, remaining 1 1/2 tablespoons milk, remaining 1 tablespoon cream, and cocoa to the melted chocolate, stirring well with a whisk. Spoon chocolate mixture into a small zip-top plastic bag. Starting with peanut butter mixture, snip a tiny hole in corner of bag; drizzle icing on half of each cookie. Repeat procedure with chocolate frosting on other half of each cookie. Let stand 10 minutes or until icing is set.