While the turkey is cooking, prepare the base for the gravy, so it's ready when the pan juices are available.
Chop the white onion into small bits.
Melt the butter in a small skillet and then stir in the chopped onions, thyme, rosemary, and balsamic vinegar. Bring to a sizzle over medium high heat and then reduce heat to low and let simmer for 30 minutes, stirring often.
Once the turkey is cooked, set aside the pan juices and skim off the fat. Pour 2 to 3 cups of the pan juices into saucepan and bring to bubbling. Stir in the onion combo and then whisk in the flour and let thicken over low heat for 4 to 5 minutes. **Substitute 2 to 3 cups chicken stock, if not making turkey.
Serve Caramelized Onion Gravy over turkey at holiday meal.