Line a baking sheet with parchment paper or aluminum foil.
Break the 9 graham cracker sheets in half. Place 9 of the squares on the parchment lines baking sheet, in a single layer.
Place 1 or 2 marshmallows over each graham cracker square.
Set the oven to broil. Place the baking sheet in the oven and toast the marshmallows for 30 - 90 seconds. Watch them closely so they do not burn.
Use an oven mitt and remove the pan from the oven. Place a piece of chocolate over each of the toasted marshmallows.
Turn the oven off. Using your oven mitt, return the baking sheet to the oven. Give the chocolate about 30 to 60 seconds to start to melt.
Remove the baking sheet and place the reserved graham cracker square on top of the melted chocolate.
Serve immediately or cool before serving.
Notes
Keep a real close eye on the oven while the marshmallows toast. They can burn very easily. Store any left over s'mores in a Zip-loc bag or an airtight container at room temperature. You can reheat the s'mores in the microwave, on a microwave safe plate, for about 10 seconds. The marshmallow will expand while heating.