This is not a sugar-coating on a Christmas log, but a thin and resupinate fungus which resembles whitewash.
It can be seen all year round, especially autumn to winter. Found on living and dead wood of deciduous trees, especially elder. Common and widespread.
Photographs of Elder Whitewash (Hyphodontia sambuci) taken January 2012, local wood, Staffordshire. © Pete Hillman 2012. Camera used Panasonic Lumix DMC-FZ38.