How-to Make a Yule Roll
Whip: Fluffy egg whites are key to making this cake light and airy. Add sugar slowly to avoid weighing down your whites.
Roll: While the cake is still warm, roll it into a log. (The towel keeps the cake from sticking to itself.) Keep it rolled until cool. This trains the cake to hold its final shape.
Spread: For optional bark: Use an offset spatula to thinly spread 4 to 6 oz. melted bittersweet chocolate on a parchment paper-lined baking pan. The thinner the chocolate, the easier it is to break into shards. Refrigerate until set.
Snap: This is the fun part. Get cracking. Uneven pieces add lots of barklike character. If chocolate softens, pop it back in the fridge.