Carmelized Onions

1 Tblsp. olive oil
1 Tblsp unsalted butter
1-lb. yellow onions, peeled and sliced in half-rounds
1 Tblsp. balsamic vinegar
1/4 tsp. kosher salt
1/4 tsp. ground black pepper

Heat the olive oil and butter in a large shallow pot, add the onions and thyme, and toss with the oil. Place the lid on top and cook over medium-low heat for about 10 minutes to sweat the onions. Remove the lid and continue to cook over medium-low heat, stirring occasionally, for 25 to 30 minutes, until the onions are caramelized and golden brown. If the onions are cooking too fast, lower the heat. Add the vinegar, salt, and pepper and cook for 2 more minutes, scraping the brown bits from the pan. Season to taste.

*Original recipe source: Ina Garten "Niman Ranch Burgers"