If you’re a fan of Chinese food, you know (and probably love) XO sauce. The chunky, umami-rich condiment, native to the Cantonese kitchens of Hong Kong, is made from dried seafood, cured ham, chiles, and more—including its namesake ingredient, “extra old” cognac (a luxury prized by the Hong Kong elite when the sauce was created in the 1980s). It’s more than just a flavoring agent for Thach Tran, Ace Eat Serve’s chef since August 2017: XO is an obsession that takes Tran three days to make from scratch. He starts by soaking and shredding dried scallops (“They’re $120 per pound at Pacific Ocean right now,” Tran says), salted cod, and prosciutto; then he stir-fries it all in house-made chile oil. “I like to fry the mixture until it’s really fragrant,” Tran says. “It makes the restaurant smell just like a fish and chips shop.” Next, he cooks aromatic ginger, garlic, orange peels, and smoky bonito flakes in the infused oil before finishing the mixture with cognac, soy and fish sauces, and Sriracha. The result is complex, concentrated, spicy, and savory—and best appreciated in an entrée on Tran’s menu called XO Rice Pillows. Chewy-tender rice-noodle rolls (“cheong fun”) come stir-fried with fresh shrimp and scallops, colorful veggies, lotus root, and, of course, Tran’s scrumptious XO sauce, which we’re certain will become your obsession, too.