Depending on how hot the day is, and how directly the sunlight shines on the oven, the marshmallows will take 30 to 60 minutes to get squishy when you poke them.
Then, open the oven lid and place a piece of chocolate (about half the size of the graham cracker square) on top of each marshmallow. Place another graham cracker square on top of the chocolate and press down gently to squash the marshmallow.
Close the lid of the solar oven and let the Sun heat it up for a few minutes more, just to melt the chocolate a bit.
Note that unlike most recipes, our s’mores have the marshmallow UNDER the chocolate. That’s because, in the solar oven, it takes the marshmallow longer to melt than the chocolate.
How does it work?
Solar cooking is done by means of the sun’s UV rays.
It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature, though this can somewhat affect the rate or time required to cook, but rather it is the sun’s rays that are converted to heat energy that cook the Smores.
The heat from the sun is trapped inside of your pizza box solar oven, and it starts getting very hot. Ovens like this one are called collector boxes, because they collect the sunlight inside. As it sits out in the sun, your oven eventually heats up enough to melt cheese, or cook a hot dog!
How does it happen? Rays of light are coming to the earth at an angle. The foil reflects the ray, and bounces it directly into the opening of the box. Once it has gone through the plastic wrap, it heats up the air that is trapped inside. The black paper absorbs the heat at the bottom of the oven.
Your solar oven can reach about 200° F (93.3 C) on a sunny day and will take longer to heat things than a conventional oven. Although this method will take longer, it is very easy to use, and it is safe to leave alone while the energy from the sun cooks your food.