Unlike a creme brulee, which has a custard "filling" with a crunchy, caramelized sugar top, flan has a smooth, creamy custard with a silky, soft caramel sugar top (it almost becomes a brown sugar sauce by the time it's done cooking). The combination really is divine.
This particular recipe comes straight of our cookbook, Artisanal Gluten-Free Cooking (page 223). By far the hardest part (and it's not really that hard) is taking the time to melt the sugar slowly over low heat. Attempts to accelerate the process with higher heat will only result in burned sugar, and that's worthless for making the dessert. Patience, in this case, is definitely rewarded!