This open-faced porchetta sandwich with caramelized apples is so colossal and tasty, it doesn't need a second slice of bread. Eat it with a fork and knife to get the flavor of each component in every bite of this meal.
Melt butter in a skillet over medium-low heat.
Cook apples, sugar, and water, stirring occasionally, until apples are soft and sauce has caramelized, about 20 minutes.
Top bread with heated pork, onions, and the apples. Sprinkle with watercress, and drizzle with caramelized sauce from apples and the heated reserved jus.