By Paul Reidinger

NEXT TIME YOU'RE out and about on Polkstrasse at, say, three in the morning, and hunger pangs strike – as they are wont to do in the wee hours, if other pangs haven't struck first – nip around the corner of Pine into the Grubstake. What do you notice about the place? That it's open, of course, and host to a crowd that answers to the description "colorful." You perceive too that the restaurant, despite its slightly mud-spattered, Wild West name, is anything but grubby. Cheery is more like it, in classic diner fashion – and clean. Then there's the grub, which the Grubstake has in spades: patty melts, clubs, and other such wholesome Americana.

Yes, everything seems quite in order, quite what one would expect, except that, for some reason (late-night dementia? lovelornness?) or no reason, you flip the menu over and find yourself staring at a list of Portuguese dishes – dishes with lots of bacalhau (salt cod), linguiça, and olives in them. It strikes you that, even as the fad for Spanish food continues to wax (the current Zagat lists nine Spanish restaurants in the city), the cuisine from Iberia's west coast is virtually unrepresented here (Zagat lists zero Portuguese restaurants) apart from a faint but perceptible influence, a remnant of colonial days, on the menus of Singaporean-style places like Straits Café, and of course, indirectly, in our phalanx of Brazilian restaurants. But then Portugal, like Ireland, is a small, poor country, isolated and easily overlooked on the fringes of Europe.

Even wearing its smart Portuguese cap, the Grubstake is unlikely to be mistaken for a temple of high cuisine, but the peasanty, mom's-recipe quality of the food is part of the attraction. We nearly became addicted to the caldo verde ($2.25 for a bowl), a broth thickened with pureed potato and aswirl with shreds of bright green kale and, lurking at greater depth like little attack submarines, stubby cylinders of garlicky linguiça. The soup, despite its old-world provenance, seemed to go quite naturally with the big American platters that followed: a patty melt ($5.25) – a beef patty with jack cheese and grilled onions on sourdough – and the more or less self-explanatory tuna melt ($5.25), with pleasantly nippy cheddar cheese. (Fries can be added on for $1.25.)

But the caldo verde would also nicely precede some of the bigger Portuguese-style dishes, such as the garlic shrimp ($14.25), whose tiger prawns are given a simple treatment that will seem familiar to anyone who's had the Spanish version, "a la plancha." (Crusty golden potato rounds on the side, mom-style.)

The bacalhau a gomes de sa ($13.50) – a hashlike jumble of chopped salt cod, cubed potatoes, sliced onions, parsley, bits of hard-boiled egg, and of course, black olives – is like an omelette filling in search of an omelette to fill. It has a bit of morgue pallor – white fish, white potatoes, and mostly white egg on a white platter, the only color desperately provided by the parsley and olives – but is surprisingly tasty.

There are tons of olives, too, in the Portuguese-style tomato-tuna salad ($6). In fact, the olives are the best part of the whole thing. Similar dishes turn up on European menus (especially in Italy and Spain), but they tend to use European-style tuna, packed in olive oil. The Grubstake's tuna has a whiff of Starkist about it, but even slightly shabby American-style tuna is generally tasty and low-fat – as it is here. And it also matches up well with the ambience.

The more atmospheric half of the Grubstake lies to the right of the entrance. There you'll find the bar and, near the front windows, an array of tables favorable to conversation – all of it under a low, slightly convex ceiling that promotes the illusion you're on a railroad dining car from yesteryear. Or possibly in a Quonset hut on some Pacific island (one well back from the action) in 1944. Either way, there is a sense of transition and impermanence; the place feels changeable, as all sorts of impromptu and yet quite mutually satisfying deals are struck within its narrow embrace.