Plain simple food, served quite quickly, good service, very nice setting: Sobrino de Botín. It’s in Calle Cuchilleros, southwest of the Plaza Mayor in Madrid.
It’s the oldest, still running restaurant in the world, dating 1725. There is actually evidence that the house was used as eating place since 1590. Goya worked there as dishwasher, Hemingway loved it, and me, I was just melting on my Tarta Botín.

Tarta Botín

No, it’s not pricy. For two persons, just main courses, 1/2 Jarre Sangria, bottle of water, and dessert, we had for about 60 EUR. That’s NOT much if you see the place! And you get something on your plate, not just an olive sized curiosity!
Funny fact: the waiter took away the Visa and came back for a signature. He actually gave it to me to sign, but I pointed to my sister who was paying! His expression was like first confused, then surprised, then gentle and looking to me like “wuh!?”.