How to Make It
Finely grate the zest of 2 of the oranges. Using a very sharp knife, peel all of the oranges, carefully removing all of the bitter white pith. Slice the oranges into 1/4-inch-thick rounds and arrange them in a large, shallow bowl. Drizzle the rum over the oranges and sprinkle the zest on top.
In a large saucepan, spread the sugar in an even layer. Warm over moderate heat, without stirring, until the sugar starts to melt around the edge, about 3 minutes. Reduce the heat to low and shake the pan to mix the dry sugar and melted sugar. Continue to cook over low heat, swirling the pan frequently, until all of the sugar is melted and a dark amber caramel forms. Drizzle the caramel in long, thin lines over the oranges. Let the caramel cool, then serve.