Preheat oven to 400°F.
In an 8x8-inch baking dish, medium baker, or cast iron skillet, spread the chopped dark chocolate evenly across the bottom.
Sprinkle the milk chocolate chips over the dark chocolate.
Drizzle the caramel sauce evenly over the chocolate.
Top with the mini marshmallows, covering the chocolate layer as completely as possible.
Bake for 8–12 minutes, or until the marshmallows are puffed and golden brown.
Remove from the oven and let rest for 3–5 minutes.
Sprinkle with flaky sea salt.
Serve warm with graham crackers for dipping.