I can see why you thought of brain fungi. However, those are soft and more-or-less jelly like, without distinct upper and lower surfaces. In the genus Stereum you see leathery, shelf-like growths - in some species extending more than 5 centimetres out from the wood and often more-or-less flat. In Stereum hirsutum the 'shelves' are short and wavy and often folded downward. One thing in all Stereums is that the underside of the 'shelf' is smooth - no gills, no spines, no pores. In Stereum hirsutum the upper surface is markedly hairy (albeit with short hairs) - hence the 'hirsute' part of the name.