Soak cashews in water for about an hour to soften them up, then drain.
Heat olive oil in a pot and add onion and garlic. Cook until translucent.
Add sweet potato, salt and pepper, broth, and rosemary stem. Bring to a boil, then simmer for 20-25 minutes. The rosemary will be removed so don't pull the leaves off the stem.
Let the soup cool, then remove rosemary stem.
Mix sweet potato mixture, cashews, and unsweetened plain coconut yogurt in a blender until smooth. Add more salt and pepper, if necessary.
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 the way full. Let out as much air as you can, and lay flat in the freezer.You can keep soup in the freezer 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.