For the Fish Filling:

• 1.5 lbs white fish fillets (cod, haddock, or a mix, skinless and boneless)
• 1 cup milk
• 1 bay leaf
• 1 cup frozen peas
• 1 cup diced carrots
• 1 leek (thinly sliced)

For the Creamy White Sauce:

• 1/4 cup butter
• 1/4 cup all-purpose flour
• 3 cups milk (including the milk used for poaching fish, topped up if needed)
• 1/4 teaspoon ground nutmeg
• Salt and pepper to taste
• 2 tablespoons chopped fresh parsley
• 1 tablespoon chopped fresh dill

For the Mashed Potato Topping:

• 2 lbs potatoes (peeled and quartered)
• 1/4 cup milk or cream
• 2 tablespoons butter
• Salt and pepper to taste
• 1/2 cup grated cheddar cheese (optional)