Apple Baked German Pancakes

1 tablespoon butter 1/4 cup sugar, divided 3/4 teaspoon ground cinnamon 1 large cooking apple, cored and sliced 3 eggs 1/2 cup milk 1/4 cup all-purpose flour 1/2 teaspoon salt, optional In 8- to 10-inch omelet pan or skillet with ovenproof handle over medium heat, melt butter. Stir in 3 Tbsp. of the sugar and the cinnamon. Arrange apple slices over sugar mixture in pan. Cook, turning apple slices occasionally, until crisp-tender, about 3 to 4 minutes. Beat together remaining ingredients until smooth. Pour over hot apple slices. Bake in preheated 375F oven until golden brown and sides are puffy, about 15 minutes. Serve immediately.