We were a party of 6 without a reservation on a Saturday. They were most kindly. It looked empty but this is the normal late dining thing in Madrid. We were fortunate as they just had a cancellation. It filled up pretty quickly afterwards, a reflection of how good they are.
Starters were excellent, they do a croquette starter, that would be a bit improved by having a citrus sauce contrast or something, but was great on it's own.
Everyone was more than happy with their mains,
I was the only one a little disappointed with dessert - a sorbet essentially dissolved in a cava, but nothing could take from an outstanding experience.
Finally, what made it an outstanding experience was the friendliness and efficiency of the waiter. He was competent, friendly and interested and it makes all the difference.