Cheesy Soup

Directions

1. 1
   Melt butter in heavy large saucepan over medium heat.
2. 2
   Add leek and saute until tender, about 5 minutes.
3. 3
   Add stock and potato and bring to boil.
4. 4
   Reduce heat and simmer for 25 minutes, stirring occasionally.
5. 5
   Puree soup in batches in processor or blender.
6. 6
   Return soup to the saucepan.
7. 7
   Add half-and-half and bring to simmer.
8. 8
   (Can be prepared 1 day ahead, covered and refrigerated.
9. 9
   Bring to simmer before continuing.)
10. 10
    Gradually add all cheeses to soup and whisk until melted.
11. 11
    Ladle soup into bowls and garnish with tarragon.