Prepare a square baking pan by coating it thoroughly with non-stick cooking spray or lining it with parchment paper for easy removal.

Place a large pot over medium-low heat and melt the salted butter until it is completely liquid and golden.

Pour the mini marshmallows into the melted butter and stir constantly with a silicone spatula until the mixture is smooth and creamy.

Remove the pot from the heat immediately once the marshmallows have melted to prevent them from becoming too hard.

Fold the cereal into the marshmallow mixture gently, ensuring every piece of toasted oat and colorful charm is well coated.

Transfer the sticky mixture into the prepared baking pan using a greased spatula.

Press the mixture down lightly into an even layer, being careful not to pack it too tightly so the bars remain soft.

Allow the treats to sit at room temperature until they are fully set and firm enough to slice.

Lift the block out of the pan and use a sharp, greased knife to cut the treats into squares.