Simple Fish Chowder

Name: Simple Fish Chowder
Ingredients: 3 cups white fish fillets (haddock, cod or pollock) cut into 1 1/2-inch pieces; 2 tablespoons unsalted butter; 2 large potatoes (washed and diced); 1 medium onion (chopped); 2 ribs Celery (chopped); 3 tablespoons unbleached all-purpose flour; 4 cups milk; kosher salt (to taste); freshly ground Black pepper (to taste); ½ teaspoon mustard powder; 1 teaspoon Worcestershire sauce; 1 cup light ligth cream; fresh parsley (chopped); oyster Cracker (or bread)