1. To prepare batter, lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking powder, 1 tablespoon granulated sugar, salt, and 1/8 teaspoon nutmeg in a medium bowl, stirring with a whisk. Combine egg substitute, milk, butter, and vanilla in a small bowl, stirring with a whisk. Add egg substitute mixture to flour mixture, stirring with a whisk. Let stand 30 minutes.
2. Preheat oven to 425°.
3. To prepare apple mixture, coat bottom and sides of a 10-inch ovenproof skillet with cooking spray. Combine 1/4 cup granulated sugar, cinnamon, and 1/2 teaspoon nutmeg; sprinkle evenly over bottom and sides of pan. Arrange apple in an even spokelike layer in pan. Sprinkle apple with remaining 1/4 cup granulated sugar. Cook over medium heat 8 minutes or until mixture bubbles. Slowly pour batter over apple mixture.
4. Bake at 425° for 15 minutes. Reduce oven temperature to 375° (do not remove pancake from oven); bake an additional 13 minutes or until center is set. Carefully loosen pancake with a spatula. Gently slide pancake onto a serving platter. Sift powdered sugar over top. Cut into 6 wedges; serve immediately.