1-1/2 cups fresh or frozen wild blueberries or 1 can (15 ounces) water-packed wild blueberries, well drained
1/2 cup sugar
1/3 cup all-purpose flour
1/2 teaspoon ground cinnamon
1/4 cup cold butter, cubed
Preheat oven to 375°. In a bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add egg; mix well. Combine dry ingredients; add to creamed mixture alternately with milk. Stir in vanilla. Gently fold in blueberries.
Fill greased or paper-lined muffin cups two-thirds full. For streusel topping, in a small bowl, combine the sugar, flour and cinnamon; cut in the butter until crumbly. Sprinkle over muffins. Bake until a toothpick comes out clean, 20-25 minutes.