Preheat oven to 190 degrees C. Grease muffin cups or line with paper muffin liners.
Muffins: In a large bowl, cream together the butter and sugar until light and fluffy. Stir in the eggs one at a time, beating well with each addition; then stir in the vanilla. In a separate bowl, stir together 2 cups flour, baking powder and salt.
Stir the flour mixture into egg mixture alternately with milk. Fold in blueberries. Spoon batter into prepared muffin cups.
Topping: In a small bowl, mix together 2 tablespoons flour, brown sugar and cinnamon. Cut in butter until mixture resembles coarse crumbs. Sprinkle topping over unbaked muffins.
Bake in preheated oven for 25 to 30 minutes, until a toothpick inserted into the centre of a muffin comes out clean.