For the truffle base: In a double boiler (you know the rules, don't let that water touch the bottom of your top pot or bowl), add the milk chocolate, sweetened condensed milk, bittersweet chocolate and salt. Cook until the mixture reduces in volume and slightly thickens, 8 to 10 minutes. Transfer to a tray and then refrigerate until solid, about 3 hours.
For the coating. Set the oven to broil or the highest temperature possible on your oven and preheat. On a large parchment paper-lined baking sheet with edges, add the marshmallows in 1 layer. Broil until the marshmallows are black: not brown, but black. If the oven is uneven, rotate the tray during broiling, but it needs to char them black. Have the strength to wait.
Allow the marshmallows to cool completely; sliding the parchment off the sheet onto a plate and placing it in the fridge helps. Once the marshmallows are hardened completely, remove and finely chop. Add them to a large bowl with the graham cracker crumbs and stir to combine.
Remove the truffle base from the refrigerator and, using a small scoop or spoon, make several balls a bit smaller than a golf ball or the size of a shooter marble. Roll these in the graham/marshmallow coating and place on a tray. Repeat with the rest of the truffle base and coating and refrigerate until ready to serve.
Serve the truffles chilled or at room temperature.