Preheat the grill to its highest setting.
Put the fish in a large saucepan with the milk and bay leaf. Season with black pepper, then cover. Bring the milk to a gentle simmer, over a low heat. Cook for 5-8 minutes until the fish is just cooked through (it should be opaque and flake easily). Drain the fish and flake into a bowl. Add half the cheese, the egg yolks and the mustard and gently fold together.
Season the tomatoes and cook under the grill for 5-10 minutes. After 3 minutes, add the bread and cook on both sides, until lightly toasted. Remove the toasts from under the grill. Top with the haddock mixture and the remaining cheese. Return to the grill and cook for a further 2-3 minutes or until golden. Serve the rarebits with the tomatoes scattered with the parsley.