Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8-inch baking pan.
Mix apple slices and applesauce together in a bowl. Whisk 1/2 cup melted butter and eggs together in a separate bowl; pour into apple mixture. Stir in brown sugar until well incorporated. Pour apple mixture into prepared baking pan.
Mix bread crumbs, 1/2 cup butter, white sugar, and vanilla extract together in a bowl; sprinkle over apple mixture.
Bake in the preheated oven until apples are tender and topping is lightly browned, about 30 minutes.