Line a 9 x 13" pan with parchment paper and set it aside. You can lightly spray the bottom of the pan with nonstick spray to help keep the paper in place, if needed.
Melt butter in a large pot over low heat. Separate 2 cups of marshmallows and set them aside. Add the rest of the marshmallows and stir. Continue to heat on low, stirring with a wooden spoon until the marshmallows are smooth and just melted.
8 tablespoons unsalted butter, 16 ounces mini marshmallows
Remove from heat and stir in the vanilla extract and salt.
1 teaspoon vanilla extract, ¼ teaspoon salt
Fold in the cereal, semisweet chocolate chips, graham crackers, and the remaining marshmallows that you set aside earlier. Fold together until everything is evenly coated in the melted marshmallow mixture.
16 ounces mini marshmallows, 6 cups Rice Krispies, 1 cup semisweet chocolate chips, 1 ½ cups graham crackers
Gently spread the marshmallow Rice Krispie mixture in an even layer in the prepared pan.
If desired, you can top the treats with additional graham crackers, marshmallows, and Hershey bar pieces.
Mini marshmallows, Graham crackers, Fun size Hershey’s bars
Let cool on the counter for 30 minutes to an hour before cutting into squares with a sharp knife.