Preheat oven to 375 degrees F (190 degrees C). Position rack in center of oven. Line with paper liners, or butter or spray, with a non stick cooking spray, 12 - 2 3/4 x 1 1/2 inch muffin cups.
In a large measuring cup or bowl whisk together the egg, buttermilk, oil, and vanilla extract.
In another large bowl combine the flour, sugar, baking powder, baking soda, salt, and zest. Gently fold in the berries. With a rubber spatula fold the wet ingredients into the dry ingredients and stir only until the ingredients are combined. Do not over mix the batter or tough muffins will result.
Fill each muffin cup almost full with batter, using two spoons or an ice cream scoop. Place in the oven and bake until a toothpick inserted in the center of a muffin comes out clean, about 20 - 25 minutes. Transfer to a wire rack and let cool for about 5 - 10 minutes before removing from pan.
Makes 12 regular sized muffins.
Note: If using frozen berries you may have to bake the muffins a little longer than the stated time.