Red Onion Marmalade

2 tablespoons olive oil

1 tablespoon butter

2 large red onions, thinly sliced

¼ cup white sugar

1 cup dry red wine

¼ cup balsamic vinegar

salt to taste

Heat olive oil and butter in a large skillet over medium heat; cook and stir onions and sugar in hot oil until onions start to caramelize, about 15 minutes. Stir red wine and balsamic vinegar into onion mixture and bring to a boil. Reduce heat to medium-low and simmer until liquid is evaporated, 15 to 20 minutes more. Season with salt.