These are known as “Ghost Apples.” They are created when freezing rain coats rotting apples, and when the mushy rotten apple falls out, it leaves a shell of ice.
the inside of the apple, while still cold, is probably still warmer than the frozen outside exposed to air and wind (and from rotting activity?). So the inside slush slides out the bottom due to gravity, and then the warmest part in the apple cavity becomes the next innermost part where there’s still apple. So it melting from the inside out, and freezing from the outside in. By the time it gets to the outer layer the apple has either collapsed in on itself and is no longer touching the ice, or the apple is thin enough that it doesn’t warm the ice too much (and tbe ice is being continually depleted of any heat that reaches it due to the colder outside). The apple loses mass as it starts to rot and fall out so there is also less of a heat requirement to its liquification and less of a heat transfer on the surrounding ice. It all adds up to ice shells.