Begin by boiling the chopped potatoes in a pot of water. Cook for 15-20 minutes, or until tender. Drain and mash with a little butter. Set aside.

In a separate pan, cook the white fish fillets by steaming or gently poaching them in a little water until fully cooked. Once cooked, flake the fish into small pieces, removing any bones.

In a small saucepan, cook the peas and diced carrot in boiling water for 5-7 minutes, until they are soft. Drain and set aside.

In a saucepan, melt the butter over low heat. Add the flour and stir to make a smooth paste. Gradually add the milk, stirring constantly to avoid lumps. Cook for 3-4 minutes until the sauce thickens. Add a pinch of nutmeg and black pepper if desired.

In a mixing bowl, combine the flaked fish, cooked vegetables, and sauce. Stir until well combined.

Spoon the fish mixture into a small baking dish or individual baby-sized ramekins. Top with the mashed potatoes and spread evenly. If you like, you can lightly score the top with a fork for a decorative effect.

Preheat the oven to 180°C (350°F). Bake the fish pie for 10-15 minutes, or until the top is lightly golden. Let it cool slightly before serving.

Once cooled to a safe temperature, serve the fish pie for babies in small portions. Make sure to check for any bones in the fish before serving.