In a large (at least 5 quart) soup pot over medium heat, add the butter and olive oil. Once butter is melted, add squash, onions, carrots, and garlic. Saute 5 minutes.
Add 3 cups of broth, reserving the rest.
Cover pot and simmer until squash is very tender (about one hour).
Add the cream and puree the mixture with a stick blender until very smooth (or blend in batches in blender and return to pan).
Thin with remaining broth if needed.
Fold in the crab meat and sage. Season with salt and pepper and serve.