Preheat oven to 375 degrees. Line a 12 cup muffin tin with paper liners.
Prepare the streusel. In a medium bowl, whisk to combine the light brown sugar, flour and salt.
Cut in the butter using a pastry blender or your fingertips until small and medium clumps form. You can also use a food processor. Place into the refrigerator to keep cold while preparing the muffins.
Combine the flour, salt, baking powder and baking soda into a medium bowl and whisk to combine.
Remove ¼ cup of the flour mixture and place in another bowl. Add the blueberries. Stir gently to coat the blueberries in the flour mixture. This keeps them from sinking to the bottom of the muffins.
In a measuring cup, combine the sour cream, buttermilk and vanilla extract and whisk to combine. Set aside.
In the bowl of stand mixer, cream the unsalted butter with the sugar. Mix on medium speed until light and fluffy. Don’t skimp on this step. Mix for about 5 minutes, stopping the mixer every so often to scrape down the bowl.
Add the eggs, one a time, scraping down the bowl after each addition.
Reduce mixer speed to low. Beat in flour mixture in 3 additions, alternating with the sour cream mixture, beginning and ending with flour. Mix only until just combined and well blended.
Remove the bowl from the stand mixer and fold in the blueberries and remaining flour until just combined. Fold gently to prevent crushing the blueberries and making purple batter.
Divide the batter evenly between the 12 muffin cups. I like to add a few extra berries right on top.
Sprinkle the streusel mixture on top of the muffins, dividing it evenly among the muffins.
Bake for 18-22 minutes, or until lightly golden around the edges and a toothpick comes out with a few crumbs and no wet batter.
Cool in the tin for a few minutes before placing them onto a wire rack to completely cool. Serve warm with a generous spread of salted butter.
Recipe adapted from The Dahlia Bakery Cookbook by Tom Douglas and Shelly Lance