Preheat oven to 400°. In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, one at a time, beating well after each addition. Beat in buttermilk and vanilla. In another bowl, whisk flour, baking powder and salt. Add to creamed mixture; stir just until moistened. Fold in blueberries.
Fill greased or paper-lined jumbo muffin cups two-thirds full. Mix topping ingredients; sprinkle over tops. Bake 20-25 minutes or until a toothpick inserted in center comes out clean. Cool 5 minutes before removing from pan to a wire rack. Serve warm.
For standard-size muffins: Make batter as directed; fill greased or paper-lined standard muffin cups two-thirds full. Bake in a preheated 400° oven for 15-20 minutes or until a toothpick comes out clean. Yield: about 16 standard muffins.