Onion Marmalade

• 3 medium yellow onions (about 1-1/2 lb.), sliced into thin half-moons
• 1 cup sherry vinegar or white-wine vinegar
• 1/2 cup dry white wine
• 1/4 cup granulated sugar
• 1 Tbs. finely chopped fresh thyme
• Kosher salt and ground white pepper

In a 4-quart or larger nonreactive saucepan, combine the onions, vinegar, wine, 1/2 cup water, sugar, and thyme. Bring to a boil over high heat; reduce the heat to medium low and simmer slowly, stirring occasionally, until the onions are very soft and the liquid has cooked down to a syrupy consistency, 45 minutes to 1-1/4 hours. The onions should be fairly moist but not swimming in syrup. Taste and season with salt and pepper and adjust the sugar and acid level as necessary to get a sweet-and-sour flavor. Let cool, transfer to an airtight container, and refrigerate for up to two weeks.