Heat oven to 375°F. 

Coat a 10” cast-iron pan or baking dish with butter. I used two #3 cast iron skillets which measure 5” each.

Arrange the berries on the bottom of the pan. I made one raspberry and one blueberry. You could combine berries in one larger pan.

Whisk together the flour, eggs, milk, sugar, vanilla extract in a medium bowl until smooth and the sugar has dissolved. It takes a little work to break up the flour with the whisk. I also used a fork to help break up the clumps of flour.

Pour the batter over the berries in the prepared pan/pans.

Bake 40-45 minutes or until they puff up and turn a golden brown on sides.

Cool for at least 10 minutes before serving. Be careful because the cast iron will be very hot. Also the flaugnarde will deflate when cooling. Mine was huge when I pulled it out and it looked like a lopsided balloon, but then came down in size. 

Dust with powdered sugar.