In a bowl, add sugar, butter, buttermilk, vanilla extract, and eggs. Mix until all the ingredients are well combined.
Add the flour, baking powder, baking soda, and salt. Mix until *just* combined. Do not over mix or you risk them coming out too dense.
Toss fresh or frozen blueberries in the flour until evenly coated. Toss in the batter.
Cover the bowl with a kitchen towel and let the mixture rest for at least 1 hour. If you want to get those pretty domes, do not skip this step.
Preheat oven to 425ºF. Spray a 12 cup muffin tin with nonstick cooking spray.
Divide batter evenly into the prepared muffin tin, filling each muffin cup almost to the top.
Place the muffin tin in the oven and immediately turn down the heat to 350 degrees F. The initial high heat activates the leaveners (baking soda/powder) to create those pretty domed muffins.
Bake for 20 minutes or until tooth pick inserted in the muffins comes out clean. Let cool for 5 minutes then enjoy!