1 1/2 to 2cups360-480 ml fresh blueberries (can use frozen)
Preheat oven to 375 degrees F (190 degrees C). Position rack in center of oven. Line muffin pan with paper liners, or butter or spray, with a non stick cooking spray, 12 - 2 3/4 x 1 1/2 inch muffin cups.
Mix together in a large bowl, egg, buttermilk, oil, and vanilla extract.
n another large bowl combine the flour, sugar, baking powder, baking soda, salt, and zest. Gently mix in berries and gently mix dry ingredients being careful not to over mix.
Using cupcake wrappers, make medium sized muffins, filling almost full with batter.
Mix flour sugar and cinnamon together. Using hands with mix with olive oil a little at a time to get crumb topping. You might only need a few teaspoons. I used olive oil when I ran out of butter and it worked great and no after taste.
Top each muffin with crumb topping.
Bake until toothpick comes clean, 20 - 25 minutes. Transfer to a wire rack and let cool for about 5 - 10 minutes before removing from pan.