Making from Turkey Breast Recipe: Separate the drippings from the onions. If using a cast-iron skillet, place it back onto the stove over medium-low heat. Or, place a clean skillet on the stove. Add the butter to the pan with the onions and let melt.
Making without Turkey Breast Recipe: Add 4 tablespoons butter and onions to a large skillet over medium-low heat, stirring occasionally, until the desired color is reached on the onions. It can be ready to go to the next step as soon as the onions are softened and reach a very light golden brown color, 10-15 minutes. For dark golden brown caramelized onions, this can take up to 2 hours.
Whisk in the flour and cook for 1 minute, stirring constantly.
You will need two cups of liquid, measure how much drippings you have, and add enough stock to make 2 total cups. If you are not using drippings, use 2 cups of stock. Slowly whisk in the liquid to the pan, bring to a simmer and simmer until thickened, about 3 to 5 minutes.
Take off the heat, stir in the fresh herbs. Taste, adjust seasoning if necessary.