Line an 8X8” or 9X9” baking pan with overlapping pieces of parchment paper and cut to size.
Melt the butter over medium heat in a large pot (or use the microwave method, see notes*).
Once the butter is melted, add the mini marshmallows. Stir to coat them in the melted butter.
Continue to stir until the marshmallows are completely melted.
Once the marshmallows are melted, remove them from the heat and stir in the vanilla extract.
Add the Cocoa Pebbles cereal to the marshmallow mixture. Fold it in until the cereal is completely coated.
Transfer the coated cereal mixture to the prepared baking dish, and smooth it gently into an even layer.**
Cover the dish and let the treats sit for at least 1 hour at room temperature.***
Use the parchment paper handles to lift the treats out of the baking pan. Then slice and serve the Cocoa Pebbles treats.
Store in an airtight container at room temperature for up to 3 days, or in the refrigerator for up to 5 days.