Caramelized Onions

Peel and cut the onions into julienne-size pieces. Melt the butter and oil in a large skillet. Add the onions and toss immediately to coat with butter mixture. Add the vinegar, salt, and brown sugar, and stir until salt and sugar are completely dissolved. Cook at a slow simmer until the onions are glassy and translucent. Drain off the excess liquid and allow to cool.