This recipe works best in a 4 quart / 4 liter slow cooker. You can use pears or peaches for a change in taste. If you are using very crisp apples in this recipe, like Granny Smiths or Fujis, you might want to simmer them for a few minutes before using to ensure that they soften up during cooking. I like to use Cortlands or Gravensteins, or apples that are slightly past their prime for this cake.