Put the butter in a cast iron skillet or pie dish and place it in the oven until the butter is melted.
Carefully remove the hot dish from the oven. Stir the vanilla into the hot butter, then add the dry ingredients and use the spoon to mix it all together into a dough, spreading it evenly across the bottom.
Sprinkle the blueberries on top and bake for about 25 - 30 minutes, until golden brown and set. Serve warm with whipped cream or vanilla ice cream