Coat two muffin tins in notstick spray. (Or fill with muffin papers and grease papers generously.)
Preheat the oven to 375F.
Combine sugars and butter in the bowl of a stand mixer and beat on high until smooth and fluffy, about 4-5 minutes.
Add eggs, one at a time and beat on medium speed until combined.
Add vanilla extract, salt, and baking powder with mixer on low speed and scrape down bowl to fully incorporate.
A 1/4 cup of buttermilk and mix thoroughly. Add 1 cup flour and beat until blended, scraping down the bowl if needed.
Add the remaining 1/4 cup buttermilk and 1 cup flour, beating until a soft batter forms.
Wash and mash 1 6 oz container of blueberries and gently fold into the batter.
Add an additional 6 ounces of blueberries to the batter.
Using a cookie dough scoop or 1/4 cup, dole out batter into muffin cups in equal amounts. Each muffin cup should be almost entirely full to make 12, large muffins.
OPTIONAL: Add 1-2 teaspoons of turbinado sugar evenly to the top of each muffin.
Bake for 25-30 minutes.
Let cool for 5-10 minutes before enjoying.