In a medium-size saucepan, heat the olive oil over medium heat. Add the leeks and cook until translucent, for around 5 minutes. Add the white wine and continue cooking until the alcohol evaporates and simmering slows. Add the artichoke hearts and chicken broth. Bring to a boil, then reduce the heat and simmer for 5 minutes. Remove from the heat. Add the chopped avocado and cream into a blender and blend until smooth (see note). Season with salt and pepper and serve garnished with the avocado cubes and walnuts.
Note: Take extreme care when blending hot soup in a conventional blender to prevent the soup from spraying out of the blender container. Blend in several small batches.