1. Preheat oven to 400 F.
2. Grease 12 muffin cups or line with paper liners; set aside.
3. Combine dry ingredients (including orange peel) in medium bowl.
4. Combine and add egg, orange juice, melted butter, milk, and vanilla; mix just until dry ingredients are moistened.
5. Spoon batter into prepared cups, filling each cup 1/2 full.
6. Bake 18-20 minutes, until golden brown. Let cool in pan on wire rack 5 minutes.
7. Remove from pan. Serve warm or at room temperature.