Melt the butter and pour into a large casserole dish.
Combine flour, 2 cups of the sugar, salt, baking powder, milk and vanilla.
Pour the batter over the butter.
Add the blueberries on top of the batter.
Sprinkle the remaining sugar over the blueberries.
Bake the cobbler for 1 hour and 45 minutes, or until a toothpick comes out clean from the center. (Cover with tinfoil after an hour or so, so it doesn't get too brown).