Heat oven to 350°F. Place paper baking cups in each of 24 regular-size muffin cups. In large bowl, beat all ingredients except peanut butter cups with electric mixer on low speed until moistened, scraping bowl occasionally. Beat on medium speed 2 minutes, scraping bowl occasionally.
Divide batter evenly among muffin cups, filling each 2/3 full. Press 1 peanut butter cup into batter in each cup until top edge of candy is even with batter.
Bake 18 to 28 minutes or until tops spring back when touched near center. Cool 5 minutes; remove from muffin cups. Serve warm or cool.