This all-purpose hot sauce is called xnipek, or dog's nose, because it's so spicy it makes your nose as moist as a dog's. It is prepared with two kinds of chiles, including fiery habaneros. More Mexican Recipes
Roast the jalapeños directly over an open flame or under a preheated broiler, turning, until blackened all over. Put the jalapeños in a small bowl, cover with plastic wrap and let stand for 5 minutes. Discard the blackened skins, stems and seeds; cut the jalapeños into thin strips.
In a bowl, mix the jalapeños, scallions, habaneros, cilantro and grapefruit, orange and lime juices; season with salt.
The sauce can be refrigerated for up to 1 week.