Heat butter and olive oil in a large skillet over medium heat. Add in onions and cook for 10 minutes stirring occasionally. Reduce heat and cook for an extra 10 minutes.
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Add the onions to a medium bowl along with the sour cream, cream cheese, Worcestershire sauce, balsamic vinegar, and light brown sugar. Stir until smooth and creamy. Season with salt and pepper.
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Serve this onion dip with your favorite chips, crackers, veggies, or bread!
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