In large bowl, cream butter and sugar until light. Add egg and beat well. Combine flour and baking powder. Add flour mixture to creamed mixture, alternating with milk. Stir in vanilla. Fold in blueberries. Spoon batter into greased muffin tins. For topping combine sugar, flour and cinnamon. Cut in butter until crumbly. Sprinkle on top of muffins. Bake in 375 degree oven for 25-30 minutes.