Break the graham cracker sheets in half so that you have 8 squares. Break the chocolate bars in half so that you have 4 squares.
For the Grill or Campfire:
Place the marshmallows on heat-proof skewers or sticks. Hold a few inches from the flame and toast, rotating frequently, until lightly browned all over.
Sandwich each marshmallow between 2 graham crackers and a square of chocolate. Let the marshmallow’s heat warm the chocolate for a few minutes before eating.
For the Oven:
Preheat the oven to 400°F. Place 4 graham cracker halves on a small sheet tray. Place one piece of chocolate, then a marshmallow on top of each. Bake for 4 to 6 minutes, until the marshmallow is hot and puffs up.
Top with the remaining graham cracker halves. Let cool for a couple of minutes before serving.
For the Microwave:
Place 4 graham cracker halves on a microwave-safe plate. Place one piece of chocolate, then a marshmallow on top of each. Microwave for 10 to 20 seconds, until the marshmallow is hot and puffs up.
Top with the remaining graham cracker halves. Let cool for a couple of minutes before serving.
Notes
Let the s'mores cool for a minute or two before eating. You definitely don't want molten hot marshmallows in your mouth! This short cooling period, once you've assembled your s'mores, will make the eating experience so much better (as someone who has definitely burned his tongue out of impatience, trust me!). Plus, those couple of minutes give time for the heat to transfer for perfectly melted chocolate.