Adjust an oven rack to the middle position. Preheat the oven to 450F. In a large bowl, whisk the flour, cornstarch, sugar, and salt. In a medium bowl or liquid measuring cup, whisk the eggs, milk, vanilla, and rosewater until incorporated. Whisk one-third of the wet ingredients into the flour mixture until no lumps remain, then slowly add the remaining wet ingredients, whisking until smooth.
Place the butter into a 10-inch cast-iron skillet an put it in the oven to preheat for 3 to 4 minutes, until the butter melts and starts to sizzle in the pan.
Using an over mitt, carefully remove the skillet from the oven and pour the batter in. Immediately return the skillet to the oven. Bake 16 to 20 minutes, until the edges are golden brown and crisp and the pancake has risen and puffed (if you like the edges extra crispy, you can bake it a few minutes longer).
Transfer the skillet to a wire rack and sprinkle the pancake with confectioners’ sugar. Cut into wedges and serve with fresh berries and whipped cream.