Cod with New England Clam Chowder Sauce

Name: Cod with New England Clam Chowder Sauce
Ingredients: 2 slices bacon, chopped; 2 1/2 tablespoons butter, divided; 1 small shallot, finely chopped; 1 stalk celery (keep leaves), finely chopped; 1 1/2 teaspoons all-purpose flour; 1 cup 2% milk; 1 large russet potato, peeled and diced into 1/2 inch pieces; 1 1/2 cups bottled clam juice, divided; 12 farm-raised littleneck clams, rinsed; 2 (6-8 ounce) pieces cod loin or cod fillets; salt and pepper; chopped parsley for garnish; lemon wedges for serving