Confidence: It's likely to be this, but I can't be certain.
Notes: In my understanding, which is not necessarily correct, I think this is verruculifera. The isidia look to be coralloid, some rather scattered and not confined to pustules. On my website I attempt to distinguish 'cauliflowers' and 'broccoli' - and I think this is 'broccoli'. The dark colour of the thallus lobes also suggests verruculifera, but this is not diagnostic. Looking at more populations of these difficult species is on my 'to do' list.