1. Trim the dark green tops and root ends from the leeks, then slice the white and light green parts into thin half-moons. Rinse well in cold water and drain.

2. Heat the butter and olive oil in a large pot over medium heat. Add the leeks and a pinch of salt, then cook for 8 to 10 minutes until soft and glossy.

3. Stir in the garlic and cook for 30 seconds until fragrant.

4. Add the diced potatoes and stir to coat them in the leek mixture.

5. Pour in the vegetable broth, add the bay leaf, and bring to a gentle boil.

6. Reduce the heat and simmer for 18 to 22 minutes, until the potatoes are very tender.

7. Remove the bay leaf, then blend the soup with an immersion blender until smooth or slightly chunky, depending on your preference.

8. Stir in the heavy cream, fresh dill, lemon juice, salt, and black pepper.

9. Warm gently for 2 to 3 minutes without boiling, then serve with extra dill and cracked pepper.