Heat the oil in large saucepan or dutch oven. Add garlic and leeks and saute until the leeks start to soften, about 4 minutes.
Add the potatoes and season with salt and pepper. Saute another 2 minutes.
Add broth and bay leaves and stir to combine. Bring the soup to a boil, then turn down to simmer and cook until potatoes are just tender, about 15 - 20 minutes. Stir in cashews and cook another minute.
Transfer the contents of the soup into a blender. Blend on high until smooth and creamy. Pour into bowls and garnish with chopped rosemary.
Notes
Store the soup in an airtight container in the fridge for up to 4 days, or in the freezer for up to 1 month. Reheat on the stove top or in the microwave.