Caramelized Onion-Sweet Potato Bisque

1/2c butter or vegan butter substitute 
5 large sweet onions, halved, thinly sliced (about 16 cups)
2T packed brown sugar
4 sweet potatoes or yams (about 2 1/2lb) peeled, cubed (1/2 in)
8c vegetable broth
1/2t ground allspice
1/2t dried thyme
1/2t salt
1/2t pepper

Melt butter in large pot or Dutch oven over medium heat.

Add onions and brown sugar.

Increase heat to medium-high; cook 35-40 minutes or until onions are golden brown, stirring frequently.

Add all remaining ingredients. Cook 20-25 minutes or until sweet potatoes are tender, stirring occasionally.

Blend thoroughly with a stick blender (or being very careful with a conventional blender).

8 servings.

Adapted from a recipe by Elaine Sweet, Cooking Pleasures Magazine.