Melt butter in a large pot. Add leeks, mushrooms & garlic. Saute' for approximately 5 minutes. Add clam juice, tomatoes, parsley, dill salt & pepper. Heat broth to almost boiling & add salmon. Cook salmon for approximately 3 to 5 minutes. Stir in cream & whisk in flour. Reheat. To serve, garnish w/fresh dill sprigs.