Sourced from the Wikipedia page 'Bûche de Noël'...because I live dangerously...
Bûche de Noël ("Yule log") is a traditional dessert served near Christmas (as Noel refers to the birth of Christ) in France, Belgium, Canada, Lebanon, Vietnam, and several other francophone countries and former French colonies. As the name indicates, the cake is generally prepared, presented, and garnished so as to look like a log ready for the fire used in the ancient fire-festival of the winter solstice.
The traditional bûche is made from a Génoise or other sponge cake, generally baked in a large, shallow Swiss roll pan, frosted, rolled to form a cylinder, and frosted again on the outside. The most common combination is a basic yellow sponge cake, frosted and filled with chocolate buttercream; however, many variations on the traditional recipe exist, possibly including chocolate cakes, ganache and espresso or otherwise-flavored frostings and fillings. Bûches are often served with a portion of one end of the cake cut off and set on top of the cake or protruding from its side to resemble a chopped off branch, and bark-like texture is often produced in the buttercream for further realism. This is often done by dragging a fork through the icing. These cakes are often decorated with powdered sugar to resemble snow, tree branches, fresh berries, and mushrooms made of meringue.
They can be considered a type of sweet roulade.
*Surely, the best thing about Christmas? I'm sure you'll agree. My tummy does.