It's widely believed that the best edible hangover cure is a big, greasy omelette. A more scientific-sounding cure, presented by The Food Network's Alton Brown, is to eat a piece of slightly burnt toast. The charred bits contain carbon, which help to settle a queasy stomach. But there's neither grease nor burnt bits in the most secret hangover cure lurking in the Mexican restaurants on Washington Avenue in South Philly. The cure is a massive bowl of savory sopa, and it's believed that one ingredient, menudo, is the best hangover killer in the world.

Menudo is cow's stomach. (The soup contains calf's feet, too.) This dish is not for the squeamish, or for those Americans who feel they can only eat the breast of a chicken or the fillet of the cow. That's a very bourgeois ideal, and expensive, too. To eat every part of the cow (or chicken, or what have you) is much more economical.

On a recent Sunday morning, I set out to test the hangover theory. Neither soup nor menudo are on the menu at Plaza Garibaldi, though they do serve more common hangover cures like huevos rancheros, huevos con jamon and chorizo and eggs (all $5, including coffee, only until noon).

I asked my server for soup. She said they had seafood soup, and fell silent.

Didn't they have any other varieties?

"Yes, we have pancita."

"Is that menudo?"

There was a beat as the staff exchanged looks with each other, then, finally, "Yes."

Either it's too good to share, or gringos like me are scared of menudo. I took the pancita to go, which came with chips and salsa, a stack of warm tortillas and a container of finely chopped cilantro, onions and lime wedges.

Plaza Garibaldi's sopa is very austere. The broth was as blood-red and opaque as borscht. There was no hominy or green chilies in it, no anything other than the menudo, calf's feet and some leaves that could have been basil, though traditionally the soup is made with oregano.

The sopa's scary color may be a little off-putting to a severely hungover person, or to anyone who does not subscribe to Fangoria. And the menudo looks like pieces of honeycomb, but of course it is chewy and meaty. The calf's feet look like pieces of roast duck—very fatty and delicious. And the soup is remarkably restorative. After drinking the hot, savory, faintly spicy broth and chewing on the menudo, I put a pot of coffee on and waited. Before the coffee had finished brewing I no longer felt achy or had a headache. Was it the broth? The lime juice? The tortilla? The menudo? Or just the good old-fashioned healing properties of soup?

Pancita, $10.50, at Plaza Garibaldi, 935 Washington Ave., 215-922-2370.