Filling

1. Preheat oven to 190°C / 375°F. Lightly grease a 9×13-inch baking pan. (any 3.5-4-quart baking dish)
2. Cut apples into 1-inch chunks, 1/2 inch thick
3. Mix all of the filling ingredients together in a large bowl, then spread into the baking pan.

Topping

1. Whisk the flour, brown sugar, and cinnamon together in a medium bowl.
2. Cut in the butter using a pastry cutter or fork until the mixture becomes super crumbly.
3. Stir in the oats. Sprinkle over filling.

Bake

1. Cover the baking dish and bake for 35 to 40 minutes, or until the apples are bubbling. Uncover and bake for 10 to 15 more minutes, or until the apples are tender and the topping is golden brown and lightly crisp.
2. Remove from the oven, place on a wire rack, and allow to cool for at least 5 minutes before serving. Serve warm, room temperature, or cold; plain or with vanilla ice cream.