Heat olive oil in a skillet over medium high heat; dd wings and onions and cook, flipping wings and stirring onions occasionally, until golden brown, about 10 minutes Add garlic, thyme and rosemary sprigs; add 1 ½ cups or 350ml stock to skillet and stir, scraping up any brown bits on the bottom of the panTransfer to a small stock potStir in remaining broth, carrot, celery and bay leaf; bring to a boilReduce heat to medium-low and simmer for about 1 hour, skimming occasionallyWhile broth is simmering, puree roasted onions and about ½ cup or 125ml pan juices from turkey (after roasting your turkey) in blender or food processorTransfer to a large saucepanRemove and discard wingsStrain broth through a large strainer into saucepan with onionsPress on vegetables in strainer to extract any remaining liquid; discard strained vegetablesBring strained broth and onions to a gentle boil, stirring occasionallyStir in the butter and season with salt and pepper