1Heat oven to 375°F. Place paper baking cup in each of 12 regular-size muffin cups. In medium bowl, mix buttermilk, butter and egg with spoon until blended. Stir in flours, brown sugar, cocoa, baking soda, vanilla and salt just until moistened. Stir in chocolate chips.
2Divide batter evenly among muffin cups.
3Bake 15 to 20 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes; remove from pan. Serve warm or cool.