I found this on a piece of oak this morning in the garden. I've googled but can't find a similar picture. It's about 3.5 inches in diameter and doesn't have a stalk.
I think that this may be a young form of the beefsteak fungus, Fistulina hepatica. If it is, it will develop into a thick, tongue shaped fungus which "bleeds" red liquid when it is cut. It causes a brown rot which alters the colour of oak timber and the resulting wood is valued by cabinet makers.
I have eaten this fungus, fried like a steak, and it is good.
I've never seen a beefsteak that colour before, usually got at least a red tinge even when young in my experience. Pansy could well be right and I apologise for the doubt if so but make sure you are certain before tucking in. you could always get a 'friend' to try it!
Unfortunately, it's more likely to be this one:
Please send us another photo in a few days' time
Certainly won't be having this for tea. I'll take another pic tomorrow. It still looks the same today. Thanks
Here are photos taken two days later.