Line an 8X8” or 9X9” baking pan with overlapping pieces of parchment paper, and cut to size. Lightly grease the parchment paper to hold it in place.
Add the mini marshmallows and butter to a large, microwave-safe bowl.
Melt the butter and marshmallows together in a microwave-safe bowl in 30-second intervals, stirring after each turn in the microwave.
Once the marshmallows and butter are completely melted, add in the vanilla extract and stir again.
Add the Fruity Pebbles cereal to the marshmallow mixture and fold it in until completely coated.
Transfer the coated cereal mixture to the prepared baking dish, and smooth it gently into an even layer. (**See notes)
Cover the dish and let the treats set for at least 1 hour at room temperature.***
Use the parchment paper handles to lift the treats out of the baking pan.
Slice, serve, and enjoy!
Store in an airtight container at room temperature for up to 3 days, or in the refrigerator for up to 5 days.