Preheat oven to 425°F. Grease a 12-muffin tin with butter or oil. Optional to use paper liners, but honestly, why bother? These muffins pop out perfectly, and you wont run the risk of precious pieces of muffin sticking to those paper liners.
In a large mixing bowl combine the sugar and melted butter, and beat with an electric mixer. Add the eggs, then the greek yogurt, buttermilk and vanilla extract. Mix well until nice and smooth.
Add 2 cups flour, baking powder, and salt. Mix (with a wooden spoon) until it begins to come together, but is not yet fully incorporated. You really want to avoid over-mixing in this recipe.
Toss the blueberries with a few tablespoons of flour (this step is optional, but it keeps your blueberries from sinking to the bottom of your muffins when cooking). Then fold the blueberries gently into the batter, mixing until evenly distributed. The batter will be quite thick.
Scoop your batter into prepared muffin tins, filling to the top. If using, sprinkle tops with a course sugar, such as turbinado. Bake for 5 minutes at 425°F, then lower oven temperature to 375°F and bake for another 15 minutes, until muffins are golden brown and spring back when touched. Allow to cool for 15 minutes before enjoying. Pop your muffins out carefully with a fork, cut in half, smother with butter, and devour.