Add cherry pie filling and pineapple to the bottom of the cake pan and stir to combine. Spread the mixture as evenly as possible in the bottom of the pan.
Sprinkle the dry cake mix evenly over the fruit in the pan. Break up an large lumps of cake mix.
Slice the cold butter into thin slices, 1/4-inch or thinner is ideal. Thee may be butter left if the slices were thin enough. I usually use about 10 tablespoons of butter.
Place the butter slices over the entire surface, leaving as little space as possible. Overlapping areas of butter are fine. Any spaces not covered with butter will be browned powdery bits of cake mix.
Bake for 45 to 60 minutes, or until the cake is as browned as preferred.
Serve warm or at room temperature.
Notes
Start with cold butter, it's easier to cut into slices.
Any regular size cake mix can be used, a couple of ounces in package sizing won't matter.