How to Make It
Pack the onions into a heatproof glass jar. In a medium saucepan, combine the vinegar, honey, water, lemon juice, peppercorns, 1/4 teaspoon of salt and 1 rosemary sprig and bring to a boil. Pour the hot liquid over the onions and place a small plate on top to keep them submerged. Let cool completely. Serve right away at room temperature, or refrigerate for up to 1 week.
Just before serving the onions, snip the remaining 5 rosemary sprigs into 2-inch lengths. Heat the oil in a small skillet until shimmering. Add the rosemary and fry over moderately high heat for about 30 seconds, until crisp and just beginning to brown around the edges. Drain on paper towels and sprinkle with salt. Serve with the onions.