Ah, sidra! You can't go to Asturias without trying sidra, a kind of hard apple cider, and Asturias is almost the only place you can drink it. The cider is fermented for about six months, at which point it should be drunk almost immediately, and it doesn't travel well. It's not sweet, and doesn't taste particularly strongly of apples--it's more reminiscent of new wine than anything. And it can only be had in a certain kind of place--sidra is almost its own subculture, and has its rules. Each green glass bottle has about six small servings' worth. The cider must be aerated for it to be at its best, so for each serving, the escanciador must echar un culín: the bottle must be held above the head so that it can be poured into a large, wide-mouth glass tumbler held below the waist so it breaks against the side of the glass--just enough for one big gulp (folklore has it that if globules present in the bottled sidra aren't broken up this way, they can make you nauseous). When drinking, leave just a bit in the glass, and pour out the dregs (into the troughs built into the bar for this purpose, or a wooden bucket, or the floor, which will probably have some sawdust on it). Because this libation is fairly messy, it's generally not served in fancy restaurants, but in sidrerías only (other key words to look for on signs if thirsty for sidra: chigre and llagar).
Casa Gervasio is a real old-fashioned llagar--it looks like it hasn't changed in 60 years. The decor is clean and simple, and somehow you just know you're going to get something special there. And indeed you do--sidra, of course, and some of the best, simple, Asturian cooking you'll find in Oviedo. Word is they make the best fritos de pixín around here, and it's difficult to imagine better: lightly-battered chunks of monkfish perfectly fried. They make a stupendously good chorizo a la sidra (a soft, Asturian-style chorizo stewed in--what else?--sidra), and the freshly-made tortilla española (the potato-egg cake kind of tortilla, almost like a frittata) is almost a revelation. And don't miss the homemade potato chips... look around and you'll notice a plate of them on almost every table, for good reason. Someone in that kitchen REALLY knows their way around puff pastry (hojaldre) and pastry cream... the milhojas de crema con natas is perhaps the most exquisitely delicate dessert I've had in years (even better than the tarta de hojaldre at Restaurante Panduku, just outside of Oviedo in Granda, for years my gold standard for such desserts), and the canutillos--same ingredients, different shape--are equally good. Ask what they have that day--at any one time they prepare only a portion of the large menu. You can rest assured anything you order will be fresh and expertly-prepared.
c/de Fuente de la Plata, 68
La Argoñesa 33013 Oviedo, Spain
(+34) 985 23 42 55