Line a 9×13-inch baking pan with parchment paper or foil, leaving overhang for easy removal.
Add the graham crackers in an even layer at the bottom of the pan, breaking as necessary to fit.
In a large bowl, mix the frozen whipped topping and marshmallow fluff until combined, then set aside.
Place the milk chocolate chips in a microwave-safe bowl, microwaving on 50 percent power for 90 seconds, stirring until smooth.
Spoon half the melted chocolate over the graham crackers, spreading it evenly, then sprinkle with flaky sea salt.
Add the whipped topping mixture on top of the chocolate layer, spreading evenly.
Pour the remaining melted chocolate over the whipped topping, spreading it carefully.
Finish with another layer of graham crackers, pressing down slightly.
Cover with foil or press and seal, then freeze for at least 4 hours.
When ready to serve, pull the Frozen S’mores from the pan using the overhang and cut into squares.