Preheat your oven to 415 Fahrenheit with the fan on if you have a fan assisted oven, otherwise preheat to 450.
Scrub the skin of the squash really well and also scrub the carrots well.
Peel the squash and reserve the peel to roast for garnish.
Cut the top and bottom off the squash and cut it in half.
Scoop out the seeds and reserve them as well.
Cut the squash, carrots, celery, and onions into piece roughly the same size.
Place all the prepared vegetables along with the garlic cloves on a baking sheet and toss with olive oil, salt, pepper, cinnamon, and cumin.
Remove the seeds from the inner flesh of the squash and rinse them well then pat them dry.
Place the seeds and skin on another baking sheet and toss with olive oil, salt, pepper, and a little cumin.
Place both baking sheets in the oven. Check on the seeds and skins after about 10 minutes, stir them and if any of the skins are browned and crispy remove them - remove the rest when they are brown and crisp - probably no more than 15 minutes max.
Roast the vegetables until they are tender and have some nice brown and charred spots - 25-35 minutes.
Add some stock to the blender along with some of the roasted vegetables and puree until smooth. Do this in batches and after each batch is done add it to a large pot.
You can also place everything in a large pot and puree it with an immersion blender.
Add the half & half and more stock if you want to make the soup a little thinner. Taste and adjust the seasoning as you like.
Heat the soup and serve it garnished with some sour cream thinned with a little half & half and the roasted seeds and skins.