My mom has prepared a yule log cake every Christmas I can remember. I have no idea how this tradition came to my family, as it is extremely French (“bûche de noël”), and we are not.
The cake is a simple sponge. Whole eggs are beaten thoroughly, sugar is added, then a bit of water, and finally flour and cocoa are folded in. The batter is runny, and forms a shallow, uniform, fine-textured cake after baking.
The interior icing is a buttercream made by whipping room-temperature butter into Swiss meringue. Swiss meringue is a mixture of whipped egg whites and simple syrup cooked to soft ball stage.
The exterior frosting is icing sugar beaten into lard, which makes the colour bright white, in contrast to the beige buttercream inside the log.
I dragged a fork across the exposed sides of the cake for a bit of texture.