Preheat oven to 375 degrees F.
Line a muffin tin with 12 paper liners.
Beat avocado till smooth.
Add sugar until smooth.
Add egg.
Add vanilla and sour cream
Add dry ingredients just until blended and fold in blueberries.
Divide into muffin cups.
Mix all streusel ingredients and sprinkle on top.
Bake for 25 minutes.