Preheat the oven to 325 degrees F. Spray an 8-inch square pyrex or metal pan with nonstick spray.
In a large bowl, whisk together the cornmeal, flour, sugars, salt, baking powder and baking soda.
In a small bowl, whisk together the eggs, buttermilk and vanilla. Add to the dry ingredients, then pour in the melted butter too. Mix just until incorporated (don't over-mix). Stir in 1 cup of the blueberries.
Pour the batter into the prepared pan. Scatter the remaining 1/2 cup of blueberries on top. Bake for 40 minutes, or until the edges turn golden and a toothpick inserted into the center comes out mostly clean.