Though it may not be 100% ready for prime time, according to Eater Donostia is: Status: Certified Open.
By sheer coincidence (seriously), we happened to find ourselves sitting at the bar just after 6 PM tonight. And though there may have been technical glitches in getting the food out of the tiny kitchen, the concept, the warmth of service and the tastes on the plate mean we'll be giving this place a bunch of visits in the near future.
Modeled after the great Quimet y Quimet in Barcelona, most everything that is served food-wise starts out in a can or a jar (which are for sale) or is preserved in one way, shape or form. It's presented, perhaps on a slice of bread (montadito) or on a pick (banderilla). There are bocadillos; there are tortillas; there is ham; there is cheese...the menu is long and deep - we barely made a dent. What we ate, we mostly liked (though the hand-sliced ham needs a sharper knife and...a better hand) and I would prefer some stuff more room-temperature-y as opposed to fridge cold, but that's probably a DOH thing.
There's a quite nice sherry list. Delicious cocktails made with sherry. A nice vermouth list. Cocktails made with vermouth. Cocktails made with vermouth and sherry. There are sidras (ok, ciders) including a super tart, crisp one on draught - from Michigan, no less. A number of beers. I didn't read deeply into the wine list, though it also had plenty of choices. You won't run out of things to drink or eat here, that's for sure.
The room, directly across Avenue B from Thompkins Square Park, is long and narrow, and by narrow I mean it's about as wide as the 4th floor walk-up railroad flat apartment Sig Eater and I shared for years, but they've made good use of the space. There are tiny two-tops along one wall opposite the bar, and as you walk towards the back, there's a little semi-private alcove with a dining table that holds 6 (or 8, it they're all models). And a few more tables in the back, opposite the kitchen.
Give it a week or two, then give it a try - they're even open for breakfast at 7:30 in the AM - and evidently have a local guy from the neighborhood as their barista. I have a weakness for this type of food and a weakness for sherry and vermouth, too. Donostia Kafetegia y Merkatua fits the bill and is a nice addition to the East Villages' dining and drinking options.