Heat a heavy pot over medium heat. I used a dutch oven for this recipe. Add olive oil and butter to the pot. Once the butter is melted, add the onions, leek and dried thyme and sauté gently for about 8-10 minutes until the onions turn translucent. Then add the garlic and sauté for another 3 minutes, stirring frequently. Make sure to not let any of the ingredients brown too much so adjust your heat as needed.
Add the potatoes and chicken stock to the pot and close it with a lid. Simmer for about 30 minutes.
Add the cream and parsley to the soup and stir well. Then pour the soup carefully into a blender and blend until you get a smooth consistency. Season with salt and freshly cracked pepper.
For garnish, sprinkle some chopped parsley on top and add the croutons.