This recipe is brought to us by renowned chef Lionel Poilane whom Salvador Dali referred to as "the greatest Frenchman alive."
In the bowl of a food processor fitted with the steel blade, combine herring, onion, and chopped apple. Process until completely combined. Transfer to a small bowl, and set aside.
Pour milk into a shallow dish. Add stale bread, and let soak until the bread is very soft and the milk is absorbed. Set aside.
Add olive oil, vinegar, and soaked bread to herring mixture. Stir to combine. Season with pepper. Spread toast with herring mixture. Top with apple slices, and serve