Preheat oven to 450 degrees.

Heat a cast iron skillet over low heat while preparing batter.

Melt 2 Tablespoons butter and add to blender will all ingredients except the blueberries. Blend until smooth.

Place remaining butter in skillet, turn heat to medium and add blueberries, shake skillet to mix, then pour batter over blueberries and transfer skillet to the oven.

Bake until puffed and golden, about 15 minutes.