Lightly coat the blueberries in flour and just fold them into the batter until they’re mixed. Or Put ⅓ of the batter into the muffin cups before you add the berries. Stir the berries into the rest of the batter. Spoon it on top of the partially filled muffins. We've made this recipe using this method and just filling the muffin tin. Personally, it didn't make that much of a difference.