Preheat oven to 375 degrees.
Butter muffin tins or use muffin liners.
In a small bowl, combine the streusel ingredients. Blend until mixture is crumbly.
Whisk together egg, buttermilk, oil, and vanilla.
In another bowl, combine flour, sugar baking powder, baking soda, and salt
Gently fold in berries.
Fold wet ingredients into dry.
Fill each muffin cup to the top.
Sprinkle the streusel over tops of muffins.
Bake for about 20 minutes, or until the edges of the muffins are golden brown.