Place the oil into a large pot ad heat over a medium temperature
Add the onion and leeks and sauté until soft
Add the garlic and sauté until soft
Add the thyme leaves and stir to combine
Leave to cook until fragrant and then add the stock, potatoes and bay leaves
Increase the temperature, bring to the boil and then cover and leave to simmer for 30 minutes
Turn the heat off, remove the bay leaves and leave to cool slightly
Add the mascarpone and blend with a stick blender until smooth **
Season to taste and serve hot with thyme leaves to garnish ***
Notes
* I don't peel my potatoes, but you can if you wish. Or you can sieve the soup after blending.
** If you want the soup thinner you can add some cream or stock.
*** The soup can also be served cold with croutons.