Creamy Mussel Soup

I make this soup using fresh cooked mussels
but canned mussels or even clams work too.
This is a perfect first-course soup.
Saffron adds not only its subtle flavor
but a beautiful yellow / orange color.

Ingredients:
3 pounds mussels, scrubbed and debearded
1 cup dry white wine
2 tablespoons butter
1 large leek, well rinsed and minced
1 medium celery rib, minced
2-1/2 cups fish stock or clam juice
1 teaspoon dried thyme leaves
1 bay leaf
12 black peppercoms
12 parsley stems
1 teaspoon saffron threads
1 tablespoon cornstarch
1 cup heavy cream
1/4 teaspoon salt or to taste
1/4 teaspoon ground black pepper

Directions:
In a nonreactive soup pot,
combine mussels and wine.
Bring to a boil over medium-high heat, cover,
and cook until mussels have opened, 5 to 7 minutes.
Remove mussels from shells, reserving 6 large mussels
and 6 half-shells for garnish.
Discard any mussels that don't open.
Strain cooking liquid through
a fine sieve into a large bowl.
In same soup pot, melt butter over medium heat.
Add leek and celery and cook, stirring occasionally,
until softened, about 5 minutes.
Add fish stock, thyme, bay leaf,
peppercorns, parsley, saffron,
remaining cooked mussels,
and reserved mussel liquid.
Bring to a boil, reduce heat to low,
and simmer 20 minutes.
Remove and discard bay leaf.
In a food processor or blender,
purée soup in batches until smooth
and return to soup pot. Bring to a boil.
In a small bowl, blend cornstarch
with cream and stir into soup.
Add salt and pepper and simmer,
stirring constantly, until
slightly thickened, 2 to 3 minutes.
Strain soup through a sieve into a
large saucepan and simmer over medium heat
until heated through, 3 to 5 minutes.
Divide soup among 6 soup plates and garnish
each serving with a mussel on the half-shell.