Preheat oven to 350°. Spray four mini loaf pans. In a small bowl, whisk together flour, baking powder and salt and set aside. In a large mixing bowl, combine sugar and lemon zest. Add butter and beat until light and fluffy. 

Add eggs, vanilla and milk. Add flour mixture and mix just until combine. Stir in blueberries. Spread batter evenly into prepared pan. Sprinkle with crumb topping. Bake 30-35 minutes or until a toothpick comes out clean.