In a large bowl, whisk together flour, cornmeal, sugar, baking powder, baking soda, and salt. Set aside.
In another bowl, whisk together buttermilk, eggs, and vanilla.
Make a well in the center of the dry ingredients and pour in the buttermilk mixture. Stir until just blended; a few lumps is OK. Fold in blueberries. Let batter rest while you preheat the griddle to medium/350°F.
Once the griddle is hot, stir the melted butter into the batter. Pour batter onto griddle using a small measuring cup. Cook until bubbles start to form on top and edges look dry, then flip and cook the other side until golden. Repeat with remaining batter.
Notes
If batter is too thick, stir in an additional ¼ cup buttermilk.
If pancakes are browning too quickly, turn heat down to 325°F.