03In a medium bowl, whisk together the milk, egg, yolk, and vanilla until thoroughly incorporated. Stir in the brown butter.
04In a separate medium bowl, combine the flour, sugar, baking powder and salt. Add the milk mixture all at once and stir gently. Carefully fold in the blueberries then divide the batter evenly among the prepared muffin pan.
05For the streusel topping:: Combine all three ingredients in a bowl and rub together with your fingers. Mix like this until the mixture is crumbly. Sprinkle evenly over the muffin batter in the cups.
06Bake the muffins for 20 to 22 minutes, or until golden and crisp and passes the toothpick test. Cool in the muffin pan for 15 minutes before removing. Serve warm or at room temperature.