Coat sweet potatoes with grape seed oil and place on a baking sheet lined with parchment paper, cut side up, in a 400° F oven for 30 minutes.
In a large saucepan over medium heat, add 2 Tbsp vegetable stock, onions, and celery. cook until translucent - stirring occasionally (about 3 to 5 minutes). Add garlic, basil, ginger, cumin, salt & pepper and continue to cook while stirring for 2 minutes.
Add vegetable stock and coconut milk to the onion/celery mixture and simmer for 15 to 20 minutes, or until potatoes are done roasting.
When potatoes are done roasting, scoop the flesh of the sweet potatoes into a bowl and discard the peels. Mash well and then add to the saucepan, mixing thoroughly. You may process the soup in the blender in batches to make even silkier.