Melt the butter in a pot over low heat. Once melted, add the marshmallows and stir with a spatula until completely melted. Be careful not to burn them.

Once the marshmallows are completely melted, turn off the heat and immediately add the Rice Krispies. Mix quickly as it will start to harden.

Pour the mixture into a greased mold. Grease the back of a spoon and press the mixture firmly. Let it sit at room temperature, and once cooled, cut into pieces and enjoy.