The Infallible Sweet Potato Soup (with caramelized onions)

This recipe is from The New England Soup Factory Cookbook and comes highly praised. I served this at our New Years' Eve Party this year and for my book club (we read "Freedom," by Jonathan Franzen). On both occasions, folks returned to the kitchen for seconds.

Caramelized Onions:
2 tbs salted butter
2 large spanish onions, peeled and thinly sliced
1/2 cup packed dark brown sugar
Kosher salt and freshly ground black pepper, to taste
1/4 cup balsamic vinegar

Soup
4 tbs salted butter
3 whole garlic cloves, peeled and left whole
2 cups sliced onions
2 cups sliced carrots
1/4 cup diced celery
8 medium-large sweet potatoes, peeled and cut into chunks
10 cups chicken stock (I used veggie)
1/2 cup packed brown sugar
1/2 tps ground nutmeg
2 tb worcestershire sauce
2 cups light cream
1/2 cup sweet sherry wine (I used a fruity red)
Kosher salt and freshly ground black pepper, to taste
1 1/2 cups caramelized onions

For the caramelized onions: In a large saute pan, melt the butter over medium heat. Add the onions and saute for 18 minutes. Add the brown sugar, salt and pepper. Saute an additional 10 min. Add the vinegar and continue cooking until the vinegar starts to evaporate and the onions look thick and syrupy, 8 to 10 min more. Remove from the heat and let cool. If working ahead, the onions can be stored in a tightly covered container until ready to use. (This is super important...first time I made this recipe, I left the onions in the pan. Bad Idea! It was like removing plaster...)

For the soup: In a stockpot, melt the butter over medium-high heat. Add the garlic, onions, carrots, and celery. Saute for 10 min. Add the sweet potatoes and saute 5 min more. Pour the stock over the veggies and bring to a boil. Reduce the heat to medium and simmer until the sweet potatoes are very soft, 30 to 35 min. Puree in the soup in the pot using a hand blender (Buy one if you don't have one; it will change your life) OR working batches with a regular blender until smooth. Add the brown sugar, nutmeg, worcestershire sauce, light cream, sherry (wine), salt and pepper. Puree again until well combined. Stir in the caramelized onions with a spoon.

Makes 10 (Big) servings.