1) Gently melt the dark chocolate, heating and stirring over very low heat or hot water until it barely melts.
2) Spread the chocolate into an 8" x 12" oval on parchment paper or foil.
3) Allow the chocolate to set, but not harden completely.
4) Melt the milk chocolate the same way, and mix in half the crushed graham crackers.
5) Spread the milk chocolate over the dark chocolate.
6) Sprinkle the marshmallows and the remaining crushed graham cracker pieces on top, pressing them in gently.
7) Allow the candy to cool until hardened, then break or cut it into chunks.
8) Store the candy airtight at room temperature for up to a week; freeze for longer storage.
Yield: about 2 dozen pieces.