Blueberry Coffee Cake

1.In a medium bowl, combine the 1/3 cup flour, brown sugar, and cinnamon. Add 4 tablespoons butter cut into pieces to the bowl and cut with a pastry cutter until the mixture resembles a crumble texture. Place in refrigerator.
2.Melt 8 tablespoons butter in a saucepan over medium heat. The butter will begin to foam, whisk consistently. After a couple of minutes, the butter will begin to brown; continue to whisk and remove from heat as soon as the butter begins to brown, turn an amber color and give off a nutty aroma. Immediately transfer the butter to a bowl. Set aside to cool for a few minutes.
3.Preheat oven to 350 degrees F. Spray a 8x8 inch pan. Whisk together 1 3/4 cup flour, sugar, baking powder and salt in a large bowl; set aside.
4.Whisk together milk, egg, egg yolk, and vanilla until well combined. Add the cooled brown butter and whisk until well combined.
5.Slowly add brown butter and milk mixture to the flour and stir with a wooden spoon until combined.
6.In a medium bowl, toss blueberries with 2 tablespoons of flour. Gently fold blueberries into the batter.
7.Add batter to prepared pan and sprinkle evenly with brown sugar topping. Bake for 45-55 minutes or until golden brown and toothpick inserted into the center comes out clean or just with a few crumbs attached. Serve warm or at room temperature.