1. Heat the oil in a large skillet over medium heat. Add the onions, coat with oil, and reduce heat to medium-low.
2. Season with pepper and salt and break up any big pieces with a wooden spoon.
3. Cook the onions slowly, until soft, about 30 minutes. Your goal is keep them over the heat for a long time without letting them get brown.
4. Stir in the vinegars, broth, and sugar.
5. Cook for another 10 minutes or until the liquid has been absorbed.