Preheat the oven to 375ºF. Line a muffin pan with paper liners and set aside.
To make the muffins, melt the butter in a small saucepan over medium heat. It will melt, froth, and begin to crackle. The crackling will subside and the butter will froth again and begin to brown. Remove from the heat when the butter solids become a medium brown color and the butter smells slightly nutty. Immediately pour hot butter into a small bowl to prevent further cooking and burning.
In a small bowl, whisk milk, egg, yolk, and vanilla until combined. Add brown butter and whisk to combine.
In a large bowl whisk together flour, sugar, and baking powder. Add the milk mixture and stir gently to combine. Gently fold in the blueberries. Divide the batter amongst the prepared muffin cups.
To make the topping, combine all of the ingredients in a small bowl and rub together with your fingertips until crumbly. Sprinkle evenly over the muffin batter in the cups.
Bake 18 to 20 minutes until golden and crisp and a toothpick inserted in the center of a muffin comes out clean. Cool muffins in the pan for 15 minutes before removing. Serve warm or at room temperature. Muffins will last in an airtight container for 3 days.