1. Combine graham cracker crumbs, butter, and sugar in a medium bowl. Grease inside of an 8-inch cast iron skillet. Press mixture into the bottom and up the sides of skillet. Set aside.
2. Combine chocolates in a medium heatproof bowl. Heat cream in a small saucepan until just simmering. Pour over chocolate and let sit for 1 minute. Add cinnamon and vanilla and stir until smooth. Pour into prepared crust. Freeze until chocolate sets, about 30 minutes.
3. Meanwhile, prepare marshmallow topping. Place egg whites, cream of tartar, and salt in a meticulously clean bowl of a standing mixer fitted with whisk attachment. Combine water, sugar, and corn syrup in a medium saucepan, stirring to incorporate.
4. Place a candy thermometer into saucepan, place over medium-high heat, and bring sugar mixture to a boil. Do not stir. Use a pastry brush dipped in water to dissolve any sugar crystals forming up the sides of saucepan. Once sugar mixture reaches 200° start whipping egg whites to soft peaks, about 3 minutes (continue cooking sugar mixture). Once sugar mixture has reached 240° (you will know the syrup is ready when it starts to take on a golden color around the edges, about 12 minutes total), remove syrup from heat, turn mixer to medium speed and very slowly pour syrup into egg whites in a steady stream, avoiding whisk. Once syrup is incorporated, increase speed to high and continue whipping until thick and glossy, about 8 minutes.
5. Adjust oven rack to highest position or about 4 inches from heating element. Heat oven broiler to high. Mound marshmallow topping over chilled pie or use a piping bag to decoratively pipe drops of marshmallow all over the pie. Broil until marshmallow topping is dark brown in spots, rotating as needed, about 2 minutes.
6. Serve immediately.
NOTE: For a quicker version, skip making the homemade marshmallow topping and instead use store-bought marshmallows mounded on top of the pie.