Prep your dish: Heat the oven to 350°F (175°C). Lightly butter a 9x9-inch baking dish or similar.

Slice the apples: Peel if you like (peels are fine too). Core and slice into 1/4-inch pieces. Aim for even pieces so they cook at the same rate.

Layer the apples: Spread the slices in the dish. If you have lemon, cinnamon, or a pinch of salt, sprinkle it over now to brighten the flavor.

Make the topping (cake mix version): Combine the dry cake mix with the melted butter in a bowl until it looks like damp sand with some clumps. Scatter evenly over the apples.

Make the topping (oats version): Stir the oats with the melted butter until fully coated and clumpy. Add a small pinch of salt if you have it. Spread over the apples.

Bake: Place on the center rack and bake for 35–45 minutes, until the topping is golden and the apples are bubbling at the edges. Start checking at 30 minutes.

Rest and serve: Let it cool for 10 minutes so the juices thicken. Serve warm as is, or with ice cream, whipped cream, or yogurt.