Combine 1-1/2 cups (375 mL) of the chocolate chips with corn syrup in large, heavy saucepan. Cook over low heat, stirring often, until chips are melted. Meanwhile, whisk 1/2 cup (125 mL) of the milk with corn starch until smooth; gradually whisk into remaining milk, then into chocolate mixture. Cook over medium heat, stirring constantly, for 4 minutes or until thickened.
Remove the pudding from heat. Whisk some of the hot pudding mixture with egg yolks and vanilla; stir into remaining hot pudding mixture. Cook, stirring constantly, for 2 to 4 minutes or until thick and glossy. Remove from heat and stir in butter; divide among 8 ovenproof bowls. Let cool to room temperature.
Place bowls on rimmed baking sheet. Divide marshmallows, graham cracker crumbs and remaining chocolate chips evenly among each bowl. Broil for 1 minute or just until marshmallows are golden.