Preheat oven to 350º F and lightly grease a springform pan with butter, then wrap the outside and bottom of pan tightly with aluminum foil.
In a medium bowl, whisk together flour, cinnamon and nutmeg, then add apples.
Pour lemon juice over apples and toss everything together until apples are thoroughly coated and dry mixture is distributed evenly on them.
Transfer apples to greased pan and set aside.
In a separate, large bowl, whisk together flour, oats, sugar, cinnamon and salt.
Add cubed butter and use two forks or a pastry cutter to cut butter in. Mixture should resemble coarse sand.
Sprinkle topping over apples and place in oven.
Bake for 45-55 minutes, or until topping is golden brown and apples are molten and bubbly.
Remove from oven and let cool 15 minutes before serving, top with ice cream or whipped cream.