Line a baking sheet with parchment paper to prevent the chocolate from sticking.
In a microwave-safe bowl, melt the chocolate chips in the microwave in 30-second intervals, stirring between each until completely smooth.
Once melted, add the vanilla extract to the chocolate, if using, and stir to combine.
Pour the melted chocolate onto the prepared baking sheet and spread it into an even layer with a rubber spatula.
Drizzle half of the caramel sauce over the melted chocolate, then swirl it in to create a marbled effect.
Evenly distribute the diced apples and chopped nuts on top of the chocolate layer.
Drizzle the remaining caramel sauce over the top and sprinkle with a pinch of sea salt, if desired.
Refrigerate the bark for at least 2 hours or until set.
Once set, remove from the refrigerator, break into pieces, and serve.