Scrub the sunchokes well and clean off all the dirt. Thinly slice them into 1/4 inch pieces.
Place the sliced sunchoke pieces in a bowl of cold water with lemon juice until ready.
In a large saucepan over medium-high heat, add olive oil, leeks, and shallots and cook for 5 minutes until they start to soften.
Add the garlic and cook for another 5 minutes until they start to caramelize but not brown.
Add the drained sunchoke and vegetable stock and bring to a boil. Let it simmer and cook for another 20 minutes, stirring occasionally.
Use a hand blender or food processor and puree until the soup is smooth. Check the soup for desirable consistency. It shouldn’t be too watery or thick. Cook a few extra minutes to evaporate liquid or add a splash of water to thin it.
Stir in the cream and season with salt and freshly ground pepper to taste.
Remove the soup from heat and prepare the fried sage leaves.
In a small saute pan of medium heat, add olive oil and add the sage leaves. Let them cook for about 1 minute. Drain them on paper towel and set aside.
When ready to serve, reheat the soup gently, ladle the soup into serving bowls, top with fried sage leaves, and drizzle with truffle oil.