Place the cod in a pan of salted water and bring to the boil. Simmer for 10–15 minutes, then drain and set aside to cool slightly. Remove any skin and bones and flake the fish.
Preheat the oven to 180°C (350°F) on a conventional setting. Grease an 8-by-4-inch loaf tin with butter.
Remove the crusts from the bread slices and tear each slice into pieces in a large bowl.
Add the flaked cod, eggs, double cream, tomato purée, brandy (if using), salt and freshly ground black pepper to the bowl.
Blend the mixture with a hand blender until smooth and well combined.
Pour the mixture into the prepared loaf tin. Place the tin in a larger roasting tin and carefully pour boiling water around it until it comes halfway up the sides of the loaf tin.
Bake for 45–50 minutes, or until a skewer inserted into the centre comes out clean and the centre reaches 63°C.
Remove from the oven and allow to cool to room temperature, then chill in the fridge for at least 4 hours, or overnight for best results.
Carefully unmould the terrine and slice. Serve with homemade mayonnaise, Marie Rose sauce or toasted bread slices.