PREHEAT THE OVEN to 375°F.
STIR TOGETHER the flour and milk in a large bowl.
Melt 1/4 cup of the butter and whisk it into the batter with the salt; then whisk in the egg yolks.
BEAT THE EGG WHITES with the sugar in a separate bowl until firm and glossy, then gently fold the into the batter.
HEAT THE REMAINING 1/4 cup butter in a 12-inch cast iron skillet.
Carefully pour in the batter and scatter the raisins evenly over it.
Bake the pancake in the preheated oven until puffed and golden, 20 to 25 minutes.
Using two forks, tear the pancake into serving pieces and arrange on individual plates.
Spoon some fruit onto the pancake and sprinkle powdered sugar over it.