Preheat oven to 350. Prepare muffins tins by lining with paper cups or butter cups.
1 1/2-t baking powder
1/2-c softened butter
zest one lemon
2-c fresh or frozen blueberries
Combine dry ingredients. Set aside. With electric mixer, beat butter until soft and fluffy. Add sugar and beat 3 minutes. Add eggs one at a time until incorporated. Add buttermilk, vanilla and zest. Remove bowl and add flour by hand. Do not overmix. Gently fold in blueberries and divide among prepared pans. Sprinkle evenly with prepared crumbs. Bake 22-25 minutes until tester comes out clean. Cool 5 minutes before removing from pan. Allow to cool then drizzle with lemon glaze*.
*Lemon glaze: Combine 1/4- c powdered sugar and 1-2 t fresh lemon juice until drizzle consistency.