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. Serve with toast.
Credits: BBC Good Food