Preheat oven to 400° F (about 200° C).
Peel and quarter the onion.
Cut the tops off the heads of garlic.
Spread tomatoes, onion, and garlic heads on a baking sheet.
Drizzle with oil if using. *see note 1
Roast in the oven for 35-40 minutes. *see note 2
Once the garlic has cooled enough to handle, squeeze the bulbs out into the blender.
Add the rest of the ingredients to the blender.
Blend until completely smooth.
If needed, reheat in a pot over the stove before serving.
Drizzle with cashew cream and enjoy!