Preheat the oven to 400?F. Combine the onions, garlic, and shallots in a roasting pan just large enough to hold them in a single layer. Add the olive oil and Essence and toss to coat. Roast until well browned, about 1 1/2 hours.
Remove the pan from the oven and set over two burners on medium-low heat. Add 2 cups of Chicken Stock, the sage, thyme, and salt and cook for 10 minutes, scraping up any browned bits from the bottom of the pan with a wooden spoon.
Transfer the mixture to a blender and puree until smooth, about 2 minutes.
Scrape the puree into a large pot over medium-low heat. Add the remaining 4 cups Chicken Stock and the balsamic vinegar and stir to combine. Bring to a simmer and stir in the cream. Serve with French bread.
Makes about 2 quarts, 8 servings