Heat oven to 350°F. Place paper baking cup in each of 24 regular-size muffin cups.
In large bowl, beat cupcake ingredients with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes, scraping bowl occasionally. Divide batter evenly among muffin cups.
Bake 20 to 25 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling racks. Cool completely, about 30 minutes.
In large bowl, beat butter, cocoa and powdered sugar with electric mixer on medium speed until blended. Beat in 4 tablespoons milk and 1 teaspoon peppermint extract. Beat in enough remaining milk, 1 teaspoon at a time, until frosting is smooth and spreadable. Frost cupcakes. Garnish each with 1 candy cane.