Soak cashews in enough water to cover them. Soak for at least an hour. Drain.
Slice about ½″ off the head of garlic (the pointy end), exposing the cloves, and leaving the skin on. Put the garlic in aluminum foil and drizzle a teaspoon of olive oil on top. Cover the garlic with the aluminum foil.
Put cauliflower florets on a sheet pan. Drizzle a generous amount of olive oil on top, and sprinkle salt and pepper on top. Place covered garlic on sheet pan. Roast garlic and cauliflower at 450°F for 20 - 25 minutes, or until cauliflower is starting to brown. Roast garlic another 15 - 20 minutes, or until soft and tender.
Heat a tablespoon of olive oil in a pan. Add chopped onion and cook on medium high heat until translucent.
Squeeze garlic out of skin and add to a blender. Add onion, cashews, roasted cauliflower (saving some for garnish, if desired), vegetable broth, and tamari. Blend until smooth and creamy. Pour mixture into a deep pan and bring to a boil. Reduce to a simmer, and cook for 10 minutes. Add salt and pepper to taste.
Notes
This soup will last up to 5 days in an airtight container in the fridge.To freeze, make sure to let the soup cool completely before placing it in a freezer bag or air-tight container.For freezer-safe containers, leave about an inch of space from the top. For freezer bags, fill about ¾ of the way full. Let out as much air as you can, and lay flat in the freezer.You can keep soup in the freezer for 4-6 months, but flavors in the freezer start to fade around 2 months.When you're ready to eat, let the soup thaw overnight in the fridge, then heat in a saucepan or microwave.