Softened unsalted butter and warm pure maple syrup, for serving
In a medium bowl, whisk together the flour, cornmeal, sugar, baking powder, baking soda and salt. In a small bowl, whisk the buttermilk with the egg yolk. In a medium bowl, beat the egg white until firm peaks form. Add the buttermilk mixture to the dry ingredients and stir gently with a wooden spoon until evenly moistened; there will still be some lumps. Fold in the beaten egg white and then the blueberries.
Heat a large cast-iron skillet. Add 1 tablespoon of the oil, and when it is hot, spoon 1/4 cup of the batter into the skillet for each pancake. Cook over moderate heat until browned on the bottom and bubbles appear on the surface, about 3 minutes. Flip and cook until browned on the second side, about 2 minutes longer. Keep the pancakes warm in a low oven while you continue with the remaining oil and batter. Serve the pancakes with butter and maple syrup.