In a large sauce pan combine onions, carrots and salt. Cook over medium heat until soft, about 5 minutes.
Add water and stock. Bring to a boil and reduce to a simmer. Cover and simmer for 15 minutes.
Add potatoes and cook till soft.
Add turkey, peas and mascarpone, stir well. Heat through until the mascarpone is fully melted and incorporated into soup. Ladle into bowls and serve warm.