In a small bowl, beat cream cheese, peanut butter, sugar and milk until smooth; set aside. , In a large bowl, combine sugar, flour, cocoa, baking powder, salt and baking soda. In another bowl, whisk the eggs, water, milk, oil and vanilla. Stir into dry ingredients just until moistened (batter will be thin)., Fill 12 paper-lined jumbo muffin cups half full with batter. Drop a scant tablespoonful of peanut butter mixture into center of each; cover with remaining batter. , Bake at 350° for 25-30 minutes or until a toothpick inserted into cake comes out clean. Cool 10 minutes; remove from pans to wire racks. Cool completely. , In a large bowl, combine frosting ingredients until smooth; frost cupcakes. Store in the refrigerator.