The pandemic has been good for collaboration, especially in Philly’s food circles, where chefs have taken to teaming up for special tasting menus that bring out novelty-seekers. It’s a trend that’s seen chefs guest-star at the likes of Volver, River Twice, and Stina, often for one-night-only events.

One of the city’s latest collaborations, however, has more staying power and features two staples of the American diet: tacos and doughnuts.

Those are the primary offerings at Si, a weekends-only project from Mexican-food specialist Israel Nocelo and pastry chef C.J. Cheyne, owner of Oui bakery in Old City. Head down the narrow passageway next to Oui’s cobalt-colored storefront and you’ll find Si in a gravel courtyard festooned with a piñata and a disco ball. Step up to the bakery’s back entrance to order Nocelo’s saucy, habanero-spiked cochinita tacos and Cheyne’s Mexican-tinged doughnuts, grab a seat, and crack open a Victoria lager beer.

Nocelo and Cheyne have been frequent collaborators since the pandemic. Nocelo first tapped Cheyne’s culinary abilities in 2020 as the GM at La Llorona, to bake Mexican bread for the brunch menu. While he’s since moved on to manage at General Tsao’s House in Rittenhouse, the pair continued to work together through El Mezcal Cantina, where Nocelo consulted on the menu. Cheyne makes conchas for the new Point Breeze restaurant, which bakes them to-order in a wood-fired oven and serves them with vanilla ice cream.

Nocelo argues that Mexican and French cooking share a connection: During France’s occupation of Mexico in the 1860s, cooks used local ingredients like chocolate and chilies in approximations of classic French dishes, such as crepes.

“All of these baking breads in Mexico, like tortas and cemitas, are coming from the baguettes and croissants,” he said.

Si was conceived as a creative outlet that satisfied two respective desires: Cheyne had been considering a second location for Oui, and Nocelo — who has been involved in various projects in Philly, including La Mula Terca, Tuna Bar, and Attico Rooftop — wanted to showcase Mexican street food.

The two were discussing those ideas when it occurred to Cheyne: “I have a backyard. We use it, people love it. But what if we were to make a concept out of it?” she said. “You can start small, just to test the waters by doing a pop-up, and that’s exactly what we’ve been doing.”

They briefly launched Si last winter, serving tacos and doughnuts around a campfire in the courtyard, and brought it back in April after a hiatus.

The full menu is available for dine-in or takeout on Friday through Sunday from noon to 6 p.m. or sellout. (Si‘s selection of doughnuts is available throughout the week, and Nocelo said to look for intermittent specials like breakfast tacos soon.)

Besides tacos, you can order the cochinita as a sandwich, served on a Oui baguette, as well as mayonnaise-slicked esquites or tangy, spiced fresh fruit. Si’s pregame pack includes the trappings (tortillas, salsa, habanero escabeche) for enough tacos to feed four people, plus an optional six-pack of beer. Preorder via Instagram.

Going forward, Nocelo plans to add al pastor tacos, cooked traditionally, on a vertical spit. Oui’s pastries are seasonal, and the current floral-inspired doughnut lineup features agave-chamomile, hibiscus, and lemon-poppy seed. Look for “rainbow fruit flavors” this summer.

On a recent Sunday midafternoon, Si was a quiet oasis off the bustle of Third and Race, but Nocelo intends to cultivate a “brunchy, lounge-y vibe” with cumbia music and more greenery as the weather improves.

“It’s just fun,” Nocelo said.

Si‘s menu is available Friday through Sunday at Oui, 160 N. Third St., from noon to 6 p.m.