Graham Cracker Mixture: Combine ingredients. Press firmly and evenly onto bottom of parchment paper-lined half-sheet pan.
Bake in 350°F standard oven (or 325°F convection oven) 8 to 10 min. or until firm to the touch and golden brown. Cool pan completely on wire rack. Crumble into pieces.
Chocolate Custard: Bring cream, sugar and salt to boil in heavy saucepan on medium-low heat. Place melted chocolate in medium bowl; add cream mixture. Blend with immersion blender until smooth.
Add egg yolks, 1 at a time, blending well after each addition. Stir in vanilla. Strain mixture then let stand at least 10 min. to allow bubbles to rise to the surface. Pour 4 oz. custard into each of 6 (5 to 7-oz.) clear oven-proof jars.
Place jars into deep steam table pan. Place pan on center rack of 350°F standard oven. Pour hot water around jars to 1-inch depth. Bake 20 to 22 min. or until all but the center third is firm. The center will still jiggle slightly, but will become firm as the mixture cools. Remove from pan and cool completely on wire rack. Refrigerate at least 1 hour before serving.
Divide Graham Cracker Mixture evenly over custards. Top each with 2 marshmallow pieces; brown using kitchen torch. Add 2 additional marshmallow pieces. Brown with torch on all sides. Serve immediately.