In a microwave-safe bowl, add the butter and microwave for about 30 seconds until melted.

Stir in the marshmallows with the melted butter until they are well-coated.

Microwave the mixture on high for an additional 1 to 1.5 minutes, stirring halfway through.

Remove the bowl and stir until all the marshmallows are melted and the mixture is smooth.

Gradually add the Rice Krispies cereal to the marshmallow mixture. Stir gently to coat each piece.

Lightly grease a 9x9 inch baking dish or line it with parchment paper. Pour the mixture into the dish, spreading it evenly.

Use a spatula or your hands to press the mixture down firmly.

Let the treats cool at room temperature for about 30 minutes. Once set, cut into squares and enjoy!