Preheat oven 375. Line a small baking sheet or 8x8 pan with parchment paper, foil, or a baking mat and set aside.
Cut off the tops of 4 apples. Using a knife, core the apples, creating a bowl. Using a spoon, dig out the inside. Peel and cut the remaining apple into 1/4 to 1/2 inch chunks.
In a medium bowl, combine the apple chunks sugar, cornstarch, lemon juice, vanilla, cinnamon, nutmeg and salt. Mix until combined and spoon the filling into the apples
In a small bowl, whisk together the flour, oats, brown sugar, cinnamon, baking powder, and salt. Cut in the cold butter suing a pastry blender until small clumps form (pea size). Sprinkle the streusel over the top.
Place the apples onto the baking sheet and in the oven 30-40 minute or until the crust is browning and the filling is bubbly
Remove from the oven and allow to cool for 10 minutes before serving. Top with vanilla ice cream and caramel, if desired.
