In a medium bowl, whisk together the cornmeal, flour, and sugar. In another bowl, whisk the eggs, milk, and vanilla together. Pour the wet ingredients into the dry and mix well. Add the melted butter and stir well. Gently fold in the blueberries. Pour the batter into the prepared pan (sprinkling a few extra berries on top, if you wish) and bake for 35 to 40 minutes or until set and golden brown.