Sweet onions, whether Walla Walla or Maui, are my favorite, and I use them whenever they're available. Recently I've tasted some onion jams and marmalades but none of them featured sweet onions so I decided to make some myself.
Sweet Onion Marmalade
2 pounds Maui Sweets or other sweet onions, peeled and thinly sliced
4 tablespoons unsalted butter (substitute olive oil for a vegan version)
¼ teaspoon sea salt (kosher salt works well also)
4 cloves garlic confit (optional, but it really makes a difference)
½ cup sugar
¼ cup balsamic vinegar
½ cup red wine
¼ cup rice wine vinegar
Begin by caramelizing the onions. Melt the butter (or heat the oil) in a heavy pan over medium-low heat, then add the onions. Cook slowly for four hours or so, stirring every 10-15 minutes, until the onions are completely softened and richly caramelized. Add the salt and garlic confit about three hours into cooking, crushing the cloves into a paste. Taste and adjust the salt if necessary.
When you are satisfied with the caramelized onions, add the sugar and liquids. Raise the heat to medium-high and reduce until the liquids have been mostly absorbed, stirring frequently.
Spoon the finished marmalade into sterilized jars. I used a single 500ml jar. The marmalade will keep for 7-10 days in the refrigerator. It should be served at room temperature.