1. In a large skillet, melt the butter in the olive oil over medium-high heat.
2. Add the onions, the salt and pepper.
3. Cook, stirring constantly, until the onions begin to soften, about 5 minutes.
4. Stir in the sugar and cook, scraping the browned bits off the bottom of the pan frequently, until the onions are golden brown, about 20 minutes.