Place Rice Krispie cereal in a large mixing bowl and set aside.
In a medium saucepan, melt the butter over medium heat. Continue cooking until it turns a golden color and has a nutty aroma, typically about 5-7 minutes.
Add mini marshmallows to the browned butter. Stir constantly until marshmallows are fully melted and the mixture is smooth.
Pour the melted marshmallow mixture over the Rice Krispies. Stir until the cereal is thoroughly coated.
Transfer the mixture to a lightly greased 8x8 pan. Press down firmly using a piece of wax or parchment paper to flatten.
Allow the treats to cool completely. To expedite the cooling process, you can place the pan in the refrigerator for about 5 minutes.