Add large eggs to a bowl and beat them up. Add sugar, mix and milk, mix. Add lemon zest and juice, vanilla extract and melted butter. Mix this well. Pour the wet ingredients over the dry. Mix gently just until most of the flour is incorporated. Now add the blueberries and fold gently. The batter will look a little lumpy and that’s ok as long as the flour is incorporated. You don’t want to over mix it.