• Wash, peel and cut the potatoes into thin slices. Peel the leeks and keep only the white part and chop finely. Peel the spring onions and chop only the white part.
• Place a saucepan on the fire and once it is hot, add the butter along with the olive oil and reduce the heat to half until the butter melts, being careful not to burn it.
•  Add the leeks, spring onions, potatoes and fresh thyme with a little salt and white pepper and sauté until the vegetables are wilted.
• Add the vegetable stock, cover the pot and simmer until the potatoes are tender.
• Then remove the pot from the heat, remove the fresh thyme and mash the soup with an immersion blender until it becomes velvety smooth.
• Add the cream and put the flour in a glass with a little cold water, stir to make a thick paste and pour this into the soup.
• Put the saucepan back on the heat and bring to the boil, stirring with a wooden spoon.
• Serve the potato soup hot on plates, garnish the centre with sautéed leek pieces and drizzle with a little olive oil.

For the leek garnish:

• Peel the leeks for the garnish, keeping only the white part, cut them lengthwise in half and then use a sharp knife to cut them into thin and long sticks.
• In a non-stick frying pan, once hot, add the olive oil and add the leek sticks a few at a time and sauté them until they turn golden brown.
• Remove them and place them on paper towels until you are ready to use them.