In a microwave-safe bowl, melt the butter over medium heat. Once melted, add the mini marshmallows and stir until completely melted and smooth.

Remove from the microwave and quickly stir in the Fruity Pebbles cereal until well coated.

Grease a 9x9 inch baking pan with butter or cooking spray. Press the mixture evenly into the pan using a spatula or your hands.

Allow to cool for about 10 minutes, then cut into squares and serve.