Preheat oven to 375.F or 190 C Oil and flour a square baking pan.Cream butter and sugar until fluffy. Add egg and beat well. Combine dry ingredients.
Alternate dry ingredients and milk to creamed mixture, mixing well after each addition. Begin and end with dry mixture.
Add less than a teaspoon vanilla. Mix well. Fold in blueberries. Spoon batter into square pan.
Cream butter and sugar. Add remaining ingredients. Mix until the consistency of coarse crumbs. A food processor does this very quickly. Sprinkle over blueberry batter.
Bake at 375 F or 190 C until done-about 35 minutes.