Cod and Potatoes in Rosemary Cream Sauce Recipe

Name: Cod and Potatoes in Rosemary Cream Sauce Recipe
Ingredients: 4 cod fillets (about 6 oz each), skinless and boneless; 1 lb baby potatoes, halved or quartered; 2 tbsp olive oil; 1 medium onion, finely chopped; 2 cloves garlic, minced; 1 cup heavy cream; 1/2 cup chicken broth (or vegetable broth); 1 tbsp fresh rosemary, finely chopped (or 1 tsp dried); 1 tbsp Dijon mustard (optional, for a bit of tang); Salt and pepper, to taste; 1 tbsp butter; Fresh parsley, chopped (for garnish); Lemon wedges (optional, for serving)