1. Trim the leeks, slice the white and light green parts, and wash them thoroughly to remove any grit.

2. Heat the butter and olive oil in a large pot over medium heat.

3. Add the leeks and cook for 8 to 10 minutes until soft and fragrant, stirring often.

4. Stir in the garlic, salt, black pepper, and thyme, then cook for 1 minute.

5. Add the chopped potatoes and chicken broth, then bring the soup to a gentle boil.

6. Reduce the heat and simmer for 20 to 25 minutes until the potatoes are very tender.

7. Blend the soup with an immersion blender until smooth, or blend in batches carefully in a countertop blender.

8. Return the soup to low heat and stir in the heavy cream until fully combined and warmed through.

9. Taste and adjust seasoning if needed.

10. Serve hot topped with chopped chives, croutons, and crumbled bacon if desired.