Resupinate or forming brackets, usually on Hazel branches, with whitish to brownish upper surface.  The fertile surface is white to cream and has very small round pores.  It causes a white rot. 

Taxonomy is difficult, and this may be a complex of species including S nivea, S nemoralis and other species; microscopic examination may be needed to identify with certainty (ref:.https://www.gbif.org/species/10136541) 

Photograph upper- and under-side of bracket, and in situ on host plant.  You must ensure you have identifed the host species correctly.

Hazel or other deciduous tree