Heat your oven to 425℉. Line the muffin pan with paper liners or silicone liners.
In a small bowl, add the flour, cornmeal, baking soda, baking powder and salt. Whisk well to combine.
In a large mixing bowl, add the room-temperature butter and brown sugar, mix with a mixer until the mixture is fluffy, about 3 minutes. Scrape the bowl.
Mix in the eggs and vanilla until combined.
Switch to a spatula or spoon and gradually mix in the flour mixture, alternating with the buttermilk. Start and end with the flour, mixing just until combined after each addition. Finish by scraping down the bowl to ensure everything is evenly mixed—don’t overbeat.
Gently fold in the blueberries.
Scoop the batter into the prepared muffin liners, about two-thirds full. Top the muffins with a sprinkle of turbinado sugar if using.
Bake for 5 minutes at 425℉, then lower the temperature to 350℉ and finish baking for 25-30 minutes.
Remove from the oven to a cooling rack. Serve at room temperature.
Store any leftover muffins in a sealed container for up to three days.