This is really delicious, and makes good use of leftover stock and creamed onions from Thankgiving. If you have some leftover mashed potatoes (just 2 tablespoons), you’ll make it even “creamier.”
In a large saucepan over medium heat, combine onions, stock, and thyme. Simmer, covered, about 20 minutes, stirring occasionally. Remove thyme sprigs. In batches, purée onion mixture until smooth. Return it to the pan. Whisk in potatoes (if you have some), cream, and sherry (if you like). Season to taste with salt and pepper.