Place mixture in a cast iron pan and sprinkle with remaining shredded cheese. Bake for 20 minutes until bubbly. You can broil for the last few minutes if desired.
Remove from oven, garnish with chives and serve with crackers.
Notes
✘ Make the caramelized onions ahead of time. The hardest thing about caramelizing onions in the time it takes. The onions will keep in the fridge for 2 weeks so its easy to plan ahead and have them on hand.✘ Shred the cheese at home. Freshly shredded cheese melts better because it doesn't contain the anti caking coating that bagged cheese has.✘ Use room temperature cream cheese and sour cream. Room temp ingredients are easier to mix together.✘ If you are using frozen caramelized onions, simply thaw and add to the rest of the ingredients before baking.This recipe was updated in 2024 to make a larger quantity. The original recipe used 2 ounces of Gruyère cheese and ⅓ cup of sour cream and ⅓ cup of mayo in place of the cream cheese, sour cream, and cheese quantities in this recipe. The other ingredients remained the same.