Yucatan Salsa

MAKES ABOUT 2 CUPS. Very finely chop the onion with a knife (a food processor will make it into a quickly souring mess), scoop it into a strainer and rinse under cold water. Shake off as much water as possible, then transfer to a small bowl and stir in the juice to "deflame" the onion's pungency. Set aside while you prepare the remaining ingredients. Core the tomatoes, then cut them crosswise in half and squeeze out the seeds if you want (it'll make the sauce seem less rustic). Finely dice the tomatoes by slicing them into roughly 1/4-inch pieces, then cutting each slice into small dice. Scoop into a bowl. Slice the radishes 1/16 inch thick, then chop into matchsticks or small dice. Add to the tomatoes. Carefully cut out and discard the habanero's seed pod (wear rubber gloves if your hands are sensitive to the piquancy of the chiles), mince the flesh into tiny bits, and add to the tomatoes. Bunch up the cilantro sprigs, and, with a very sharp knife, slice them 1/16 inch thick, stems and all, working from the leafy end toward the stems. Combine radishes, chile, and chopped cilantro with the tomato mixture, stir in the onion and juice mixture, taste and season with salt, and it's ready to serve in a salsa dish for spooning onto tacos, grilled fish, and the like. Note: Jalapenos and serranos (3 to 5) can replace the habanero. Manzano chiles (1/2 to 1) also would taste good in this salsa.