Gather your rice cereal, marshmallows, butter, vanilla, and optional add-ins to keep everything within reach.
In a large saucepan, melt the butter over low heat, listening for a gentle sizzle and watching it turn glossy.
Add the marshmallows to the melted butter, stirring constantly until they’re completely melted and the mixture is smooth, shiny, and beginning to bubble gently.
Remove the saucepan from heat and stir in the vanilla extract for added aroma and flavor.
Pour the marshmallow mixture over the rice cereal in the large mixing bowl, then gently fold with a spatula to coat every piece evenly—this mixture should be sticky and glossy.
If using, stir in chocolate chips, nuts, or pretzels now to add crunch and surprise textures.
Transfer the mixture into a greased 9x13 inch pan, then press down firmly with a spatula or wax paper to flatten and evenly distribute the treats.
Let the treats cool at room temperature for at least 30 minutes until they’re firm and set—this helps them cut cleanly.
Once cooled, cut into squares or bars with a sharp knife, revealing the crunchy, chewy interior and crispy exterior.
Serve and enjoy these nostalgic, yet playful, monster rice krispie treats—perfect for sharing!
