Preheat the oven to 375 degrees. Line 18 muffin cups with paper liners or spray with cooking spray. Set pan aside.

Place 6 tablespoons of the butter in a pan with a light bottom (so you can see when the butter starts to brown). Set the pan over medium heat and melt the butter, swirling the pan occasionally to ensure the butter melts evenly. Once it’s fully melted, begin stirring with a whisk. The butter will begin to foam, deepen in color, and little flecks of brown will start to come up from the bottom of the pan. Remove from the heat a few seconds after those flecks appear, but continue whisking for another 30 or 40 seconds. Pour into a small bowl, leaving as many of those brown flecks as possible in the pan. Allow butter to cool to room temperature before finishing the muffins.

While brown butter is cooling, make the topping. Combine the all ingredients except butter in a medium bowl. Stir in the melted butter until the mixture forms clumps about the size of peas. Set aside.

Once brown butter has cooled, finish the muffins. Whisk together the flour, baking powder, cinnamon, and salt in a medium bowl. Combine the sugar, eggs, egg yolk, and cooled brown butter in a large bowl and beat on low speed with an electric mixer until combined. Melt the remaining 2 tablespoons butter and beat into the mixture. Beat in the milk and vanilla. Add the flour mixture, then beat on low speed until flour is fully incorporated. Gently fold in the blueberries.

Divide batter evenly between the prepared muffin cups, filling each cup about 3/4 of the way full. Sprinkle each with crumb topping and bake for 25 to 30 minutes, until a toothpick inserted into the center comes out clean. Let cool in pan for 10 minutes, then serve and enjoy.