Preheat the oven to 375 degrees Fahrenheit. In a large oven-safe skillet, melt 2 tablespoons unsalted butter over medium heat. Add 2 large chopped sweet onions and cook until soft and tender, about 15 minutes.
Remove the skillet from the heat and add 1 cup mayonnaise, 4 ounces softened cream cheese, 1 teaspoon garlic powder, 1 teaspoon dried thyme, ½ teaspoon salt, 1 cup shredded cheddar cheese, and 1 cup shredded smoked gouda cheese. Stir to combine.
Place the skillet in the oven and bake for 25 minutes or until bubbly. Garnish with chopped parsley and serve with crackers, crostini, or bread.
Notes
Storing Leftovers
In the Refrigerator: Place any leftovers in an airtight container in the fridge for up to 2 days. This Tennessee onion dip does not freeze well.
To Reheat: Reheat in the microwave or oven on low heat until the cheese is melted.