Prepare roasted garlic while you prepare the veggies.
In a large (at least 5 quart) stockpot, heat olive oil over medium heat. Add butternut squash, onions, carrots, celery and garlic, and sauté 5 minutes.
Add 3 cups of broth, reserving the rest. Cover pot and reduce heat to medium-low and simmer until squash is very tender (about 30 minutes).
Add the half-and-half (or milk) and puree the mixture with an immersion blender until very smooth (or blend in batches in blender and return to pan). Thin with remaining broth if desired.
Fold in the crabmeat and sage.