Heat oven to 350°F. Place paper baking cup in each of 18 regular-size muffin cups. In large bowl, mix flour, granulated sugar, cocoa, baking soda and salt. In medium bowl, mix buttermilk, oil, 1 teaspoon of the vanilla and the egg with whisk until blended. Add oil mixture to flour mixture, stirring just until blended. Divide batter evenly among muffin cups.