A tiny cream, yellowish or buff-coloured cup or disc-shaped fungus associated with decaying acorn cups.  It can have long or short stalks and usually grows in clusters.   

This species or a related species in a species aggregate has also occasionally recorded on beech mast in Leicestershire.

Photograph on host plant; note substrate and associated plant species.  

On acorns, possibly other nuts?

Autumn.

This may be an aggregate of species; we are not sure whether the specimens on beech mast or hazel nuts are now regarded as separate species. (see Laessoe & Petersen, 2019)