• Preheat the oven to 400°F. Line a standard muffin tin with paper liners.

Brown the butter:

• In a small stainless steel skillet set over medium heat, melt the butter. Swirling the pan occasionally, continue to cook the butter. It should become foamy with audible cracking and popping noises.
• Once the crackling stops, continue to swirl the pan until the butter develops a nutty aroma and brown bits start to form at the bottom. Once the bits are amber in color, about 2 to 3 minutes after the popping stops, remove from heat and pour into a medium mixing bowl, being sure to get all the toasted bits on the bottom. Set aside to cool.

Make the crumb topping:

• While the brown butter cools, combine all the topping ingredients in a small bowl. Mix with a fork until the texture resembles wet sand.

Make the batter:

• In a large bowl, whisk together the flour, sugars, salt, and baking powder.
• In a medium bowl, whisk together the cooled browned butter, buttermilk, egg, and vanilla. Pour into the dry ingredients and stir with a rubber spatula until just combined. Gently stir in the blueberries. Do not overmix. Batter will be thick. Divide evenly among the muffin tin cups.
• Use your fingertips to sprinkle the crumb topping over the muffin batter in pans. Bake until golden brown and a toothpick inserted in the center comes out clean, about 20 to 22 minutes. Transfer the pan to a wire rack to cool for 5 minutes before removing the muffins to the rack to cool completely.
• Serve or store in an airtight at room temperature for 3 days. Reheat in the microwave for about 15 seconds if desired. Muffins can also be frozen in an airtight container for up to 3 months.