Muffin Batter:

1/3 c. sugar
1/4 c. butter, softened
1 egg, beaten
2 1/3 c. flour
4 tsp. baking powder
1/2 tsp. salt
1 c. milk
1 tsp. vanilla extract
1 1/2 c. fresh or frozen blueberries

In a mixing bowl cream sugar and butter. Add egg; mix well. Combine flour, baking powder and salt; add to the creamed mixture alternately with milk. Stir in vanilla. Fold in blueberries. Fill 12 greased or paper-lined muffin cups two-thirds full. Sprinkle with streusel mix.

Streusel:

1/2 c. sugar
1/3 c. flour
1/2 tsp. ground cinnamon
1/4 c. butter

In a small bowl combine sugar, flour and cinnamon; cut in butter until crumbly. Sprinkle over muffins.

Bake at 375°F for 25-30 minutes or until browned.