Found today at Danby on dead birch branch. Spongy texture and reddish pores (with a margin around the underside lacking pores). A drop of KOH turned violet, as per Buczacki p494. ID based solely on macro features.
Top side after addition of drop of KOH
EDIT: thanks Doug. Yes, spores appear to confirm at 3.5 × 2.4 µm