I've died and gone to mushroom identification hell. I eat about 4 varieties of mushrooms from the garden, including the one pictured above, said to be edible by our helper. It turned out to be tough and spongy, but it makes a good "soup bone", tossed in a pot to make broth, and later removed. Don't judge me for eating strange mushrooms, please.
I stayed up all night last night looking for its identity, saw many that resembled it, but none with its underside!