In a large skillet over medium heat, heat butter and oil. Add onions, salt, and pepper. After about 5 minutes, or when the onions begin to soften, add Worcestershire sauce, thyme, and garlic. Stir well. Allow the mixture to continue cooking for 25-30 minutes, stirring occasionally, until the onions are dark brown. Remove onions from heat and let cool.
In a large bowl, mix Greek yogurt and cream cheese until smooth. Fold in the carmelized onions. Spoon a generous amount of the mixture into a serving dish and grab your favorite bag of chips for dipping. Then, dig in!