Peel and slice the apples to fill a 9x13 baking dish.
Sprinkle vanilla extract over the apples.
Mix butter, oats, flour, sugar, cinnamon, and nutmeg until crumbly.
Spread crumb mixture over the apples.
Bake in a 375 degree oven for 60-70 minutes, until apples are soft and topping is browned.
Serve warm with vanilla ice cream.
Can be made a day ahead and re-heated.