Lunch time is busy at Horseman's Haven, located far south on Cerrillos Road. The wood-panel ceiling and booths give the restaurant the feel of a Western saloon, and the mounted light fixtures illuminating the black and white and sepia photos filling the walls have an old-time New Mexican edge.

Today's special is beef ribs braised in red chile sauce, but a good number of the plates that the wait staff carry to patrons are covered in green. Horseman's Haven is known for its particularly hot green chile sauce. The burn starts at the back of your throat and ignites a cough, tossing heat across the rest of your mouth like napalm spreading across your tongue and palate.

The Level Two sauce, as it's known, has been around since the restaurant opened in 1981. It was created by Rose Romero, who opened the restaurant and grew up in the Española/Chimayo area. Like many households in the state, chile was a staple of the Romero household, and Rose wanted to create something that left a burning impression.

"I personally don't eat it," says Romero's daughter, Kim Gonzales, with a sly smile. "All green chile gives me heartburn."

But plenty of people do eat it. Gonzales says the restaurant ships its Level Two sauce all over the country, often to people who lived in New Mexico at one point and never forgot it. Gonzales says it's become a tradition for people to gradually build up their tolerance to it, at first ordering it on the side for light dipping and working their way up to slathering it on enchiladas and burgers. Students from St. John's College, she says, have challenged each other to formal Level Two eating contests for years.

Gonzales says the sauce is based in a pepper seed that is a hybrid of two varieties of green chiles, the Sandia and the Big Jim. Both were developed by researchers at New Mexico State University; Sandia is the hotter strain, and is about three times spicier than your average jalapeño, according to PepperScale.com.

The resulting seed gives off a satisfyingly severe burn without dilating your esophagus too much. If you happen to ingest more than you can handle, Gonzales says the key to extinguishing the fire is anything high in sugar, like jelly or honey (which, thankfully, Horseman's Haven carries plenty of—it goes on sopaipillas). The idea that chugging milk will extinguish the burning is a myth, she says.

I order a cheeseburger with the Level Two sauce on the side. Somebody brings out a plate with a large patty covered in sizzling cheddar cheese atop a toasted bun, and a small cup of green sauce.

Twelve years ago, I managed to eat a plate of "atomic" chicken wings in under five minutes at a Buffalo Wild Wings in Texas. They mounted my victorious portrait on the wall. But I approach the lab-engineered green with caution; the intentional craftsmanship demands greater reverence than garbage fast-casual wings.

I submerge one of the mashed-up potato wedges on my plate into the sauce. Hmm. Tasty, but not much kick. I ask a staffer if she's sure she brought me Level Two; oops, no, that's the regular green chile. She returns in a few minutes with the actual Level Two. I pick up my burger and impatiently dunk it into the sauce. I bite down on the chile-soaked corner of the burger.

It's bad, but not as bad as you'd expect. Once your mouth is thoroughly coated in heat, it's entirely bearable, except for the spot where the sauce makes initial contact. The heaviness of the bread and meat seemed to dull the power of the heat in a way that the fries do not. I was able to pour a new hit of sauce onto nearly every bite of the burger I took, interspersing dunks into cold ketchup to ease the intensity.

It was a satisfying lunch, though I had to breathe through my mouth for most of it to keep my face hole cool. Would I have endured this had I not been on assignment? Maybe. Level Two was tastier and more enlivening than its milder counterpart. Mixing them both together would probably make for a less intense but still enjoyable experience.

I mopped up sauce with the last bit of bun left on my plate, leaving a few centimeters on the right side of my lips comfortably aflame until well after I left the restaurant. The restaurant sells full pints of the chile for $8.50 and half pints for $4.25. I took three of the latter to go.

Even as the season to buy a bag of freshly roasted chile in a parking lot is coming to an end in Santa Fe, you can get Level Two at Horseman's Haven all year. Gonzales says they order enough of the special chiles from producers in Hatch to ensure they never run out. A seasonal batch usually reaches its peak heat in late winter and early spring, Gonzales claims.

"It seems like the longer they sit, the hotter they get," she says. "If it's not hot, it's bell peppers. That's what my mom would say."