In a mixing bowl, beat eggs. Gradually add sugar, oil, and vanilla.
In a separate bowl mix all dry ingredients. Alternate adding the dry ingredients and the sour cream into the egg mixture until combined. Gently fold in blueberries.
For the crumb, mix together flour, sugar, and softened butter until a crumb is formed. It will be a sand-like texture. Sprinkle over top of the muffins before baking.