Sauté aromatics - Heat the oil and melt the butter in a large heavy based pot over medium heat. Cook the onion, leek and garlic for 5 minutes until softened.

Add the sweet potato and cumin, cook for another 3 minutes, stirring regularly.

Simmer 20 minutes - Add the stock, salt and pepper. Bring to a simmer, then cook for 20 minutes at a gentle simmer until the sweet potato is very tender (no lid).

Blitz - Remove the pot from the stove. Blitz with a hand-held stick until smooth. (Note 4 for blender) Stir in cream.

Garnish - Ladle into bowls. Drizzle with yogurt, cream or olive oil with a sprinkle of something crunchy - pictured with pistachios and crispy flatbread strips (Note 3).