Add mini marshmallows one cup at a time stirring to melt.
You can add the pan back to the heat as needed to melt the marshmallows. Melting the marshmallows slowly will result in a softer treat.
Once the marshmallows have melted into the butter, add the salt and vanilla.
Stir in the rice cereal.
Coat the bottom and sides of an 8" x 8" pan with a thin layer of oil. I use a paper towel to wipe out the excess.
Add half of the rice cereal and marshmallow mixture to the pan.
Use a rubber spatula to press it down into a flat layer.
Cover this layer with mini chocolate chips. You'll want to use more than the picture below. I wanted our chocolate layer to be thicker than we got. (That's what happens when you let the kids be in charge of adding the chocolate chips.)
Add another layer of the rice cereal and marshmallow mixture.
Press down firmly to make sure the layers all stick together.
Top with M&M's, other candies, or more chocolate chips.
Allow the edible sedimentary rocks to cool for at least an hour. Cut into squares and serve.