Drizzle olive oil in a large, heavy-bottomed pot over medium heat. Add the onion and sweat for a couple minutes until fragrant. Add the celery, leek and garlic cloves, and sauté for about five minutes. Add the sweet potatoes, apples and the rest of the spices, and sauté for a few more minutes. Add the chicken stock and let simmer for about twenty minutes uncovered until the sweet potatoes are tender. Add the honey and simmer for a couple minutes. Remove the cinnamon sticks and cloves. Using a blender, purée soup until smooth and return to the pot.Season with salt and pepper. Ladle into a soup bowl and garnish with chopped celery leaves.