Also called a German pancake, this egg-leavened breakfast dish is like a sweeter version of Yorkshire pudding and a close cousin of the popover.
Sift flour into a medium-size bowl; then stir in sugar, cinnamon, and salt.
In a separate bowl, whisk together eggs and milk for about 1 minute; mixture should be frothy.
Preheat oven to 425°F and set a rack in the middle position. Melt butter in a 12-inch skillet over medium heat. Lay apple slices in butter and cook, without stirring, 2 minutes. Gently flip slices and cook until tender, about 2 minutes longer.
Working quickly, add flour mixture to egg mixture and whisk just to combine. Pour batter into hot skillet with apples, then transfer the skillet to oven.
Bake until pancake is puffed and golden, 10–14 minutes. Sprinkle with confectioners’ sugar and serve immediately from skillet.