Set the oven to 350°F and coat the bottom of a 13x9-inch, 3-quart glass baking dish or a 3-quart casserole with cooking spray. A light coating helps release the sticky fruit when you serve the dessert.

Spoon both cans of cherry pie filling into the prepared dish and level the fruit with a spatula. An even bed of cherries and syrup gives the chocolate layer moisture across the pan.

Scatter the dry cake mix over the filling, then gently shake the dish from side to side to level it without pressing or stirring. The surface should look loose and evenly covered rather than piled into thick mounds.

Drizzle the melted butter in slow zigzags over the cake mix, then carefully tilt the dish to spread it across as much of the surface as possible. Broad butter coverage helps limit powdery patches and encourages a crisp chocolate crust.

Bake for 42 to 45 minutes, checking that the topping looks mostly dry and the fruit bubbles around the edges before removing the dish. Look for active red syrup bubbles, a set, slightly crackled surface, and a fragrant cocoa aroma.

Leave the baked dessert to cool for 45 minutes before scooping. The filling thickens as it rests, so each serving holds together better than it would straight from the oven.