Spray a 9 x 13 baking dish with cooking spray and set aside.

In a large saucepan over medium heat melt the butter and mini marshmallows. Stir frequently until they have melted are are well combined.

Remove the saucepan from the heat and add in the Lucky Charms. Quickly stir until the cereal is combined with the marshmallows.

Pour into the prepared pan and press down lightly to even it out.

Quickly pour on the sprinkles.

Allow the treats to harden for 15 minutes then cut into 18 squares and enjoy!