Preheat oven to 350 degrees F.

Put the butter in a skillet over low heat (don’t use a dark or non-stick pan.) Let melt and cook until browned and fragrant, stirring. You'll know it's ready because it will be very fragrant with flecks of brown throughout. Pour into a glass measuring cup and set aside, making sure to get all those brown bits.

Combine the flour, sugar, baking soda, salt, and nutmeg in a large bowl and stir. Add the blueberries.

In a separate bowl, combine the eggs, sour cream, buttermilk, and vanilla. Mix well and stir in the butter. Add this mixture in with the dry ingredients and stir until combined, but don't over mix.

Lightly spray a muffin tin with cooking spray. Fill the muffin tins with the batter. Sprinkle with coarse sugar. Bake for 12-15 minutes, until tops are lightly browned.