Cut the butter into cubes. Melt butter in a saucepan over medium heat. When the butter begins to foam whisk consistently. Cook till the butter begins to brown and remove from the heat (Amber color brown butter has a nutty aroma). Cool completely
Preheat oven to 350 degrees F. Add parchment paper to the cake pan and grease with butter or cooking spray
For the topping, In a medium bowl, combine the flour, brown sugar, and cinnamon. Add the room temperature softened butter cubes to the bowl and rub together with fingers
In a mixing bowl add the dry ingredients and mix well for even mixing
In a separate bowl whisk together milk, egg, egg yolk, and vanilla until well combined. Add the cooled brown butter and mix well
Add the dry ingredients to the wet mixture and mix until combined
In a medium bowl, gently toss blueberries with 2 tablespoon of flour. Add blueberry - flour mixture into the batter
Add batter to prepared pan and add sugar + flour topping over the cake batter. Bake for 45-55 minutes or until golden brown and toothpick inserted into the center comes out clean