If you’d like a little more richness, you can brush the muffin cups with extra melted butter before adding the cheese, but keep in mind that still counts within the original four ingredients. For a slightly different flavor, swap half of the cheddar for another cheese that melts well, such as Colby or Monterey Jack—just don’t add more than one extra cheese if you’re trying to honor the simple spirit of the recipe. You can also change the character of the dish by using Yukon Gold potatoes for a creamier interior and russets for a fluffier, more layered bite. To make ahead for a holiday meal, bake the stacks until just tender, cool, cover, and refrigerate; then reheat uncovered at 375°F until hot and crisp around the edges. If you have leftovers, they reheat nicely in a skillet over medium heat, cut side down, until warmed through and re-crisped. For smaller gatherings, halve the recipe and bake in the middle cups of the pan so they brown more evenly.