In a 6~quart heavy~bottom soup pot or Dutch oven, heat the oil over medium heat. Stir in the onions.
Cover, reduce the heat, and braise for 15 minutes, checking that the onions don't burn.
Add the squash to the onions. Sprinkle with the salt, pepper, cumin and thyme; cover the pot.
Braise for another 15 minutes, checking once in a while that the vegetables do not burn. Adjust heat as needed.
Add the broth, stir the ingredients, and bring to a boil. Cover the pot and reduce the heat. Simmer for 30 minutes or until the squash is tender.
Puree the soup in a blender in batches or use an immersion blender. Process the soup until it is very smooth.
Return the soup to the pot and reheat. Taste for salt and add more cumin to taste.
Serve the soup very hot. Garnish with the toasted croutons or chopped herbs.