Heat the olive oil in a large pot on a medium heat. Add the sliced leek and sauté until tender.
Add the onion and garlic to the pan and sauté until tender and fragrant.
Add the cauliflower, sage leaves, salt, pepper and chicken stock to the pan and bring to a boil. Reduce heat to low and simmer with the lid on until the cauliflower is tender and falls apart easily.
Once cauliflower is cooked, turn off heat and remove lid. Allow to cool to room temperature before adding the almond milk. Transfer to a benchtop blender or use a stick blender to blend until smooth and creamy.
Meanwhile, make crispy fried sage leaves by adding 4 tablespoons of oil to a small cast iron frypan. Once oil is hot, add a sage leave, one at a time. Fry on one side until there are no bubbles. Flip using a spoon and fry until there are no bubbles. Transfer to a paper towel lined plate. Repeat this step with remaining sage leaves.
Reheat to serve. Serve topped with cashew sour cream and crispy sage leaves.