Arrange a rack in the middle of the oven and heat the oven to 350°F.
Lightly coat a 9x13-inch baking dish with unsalted butter.
Layer in the baking dish in the following order (do not stir together): Spread 2 (about 21-ounce) cans apple pie filling into an even layer.
Sprinkle evenly with 1 (15.25-ounce) box yellow cake mix.
Cut 1 ½ sticks unsalted butter into thin slices and arrange over the cake mix in an even layer, covering the entire surface.
Bake until golden brown, bubbling, and a crispy crust begins to form, about 1 hour.
Serve warm with vanilla ice cream if desired.
