If this is not blistered cup fungus (Peziza vesiculosa) then it is a relative.
Blistered cup grows in clusters on rich soil, manure or woodchip. People seem to commonly find it in their gardens on composted areas.
We found it on the remains of a fire that some visitor to the wood had doused with earth. This doesn’t quite meet the description of its favoured habitat but seems to be the most likely identification.