A V.
Yelp
There are two maybe three other tapas and pintxos bars that serve mushrooms on and in the Calle Laurel neighborhood, but Bar Soriano is the one I fell in love with at first bite. It's a pleasure watching them make their specialty tapa, which is mushrooms grilled in olive oil and sauteed in their secret sauce then topped with one grilled shrimp.
Everyone eats their tapa differently, but I think the secret is to let the sauce drip onto your bread, so you don't dribble it all over yourself, although part of the fun is letting the sauce dribble all over yourself, isn't it?
An old school classic, I can keep coming back to.