Lightly grease a 9-inch square pan with a teaspoon or two of butter. Set aside.
Measure the butter for the treats directly into a large heatproof microwavable bowl. Heat the butter on medium power until melted, about 1 minute.
¼ cup salted butter
Stir the mini marshmallows in the melted butter, scooping the butter up from the bottom of the bowl to coat the marshmallows.
4 ½ cups mini marshmallows
Return the bowl to the microwave and heat the marshmallows until puffy and doubled in size, about 1 to 2 minutes. Give them a brisk stir with a spoon or spatula. If there are still pieces of marshmallow return the bowl to the microwave in 30 second bursts.
Once the marshmallows are fully melted and stirred smooth, add the vanilla and salt. Stir well, and then add the cereal. Continue to stir, making sure all of the cereal is evenly coated with melted marshmallows before scooping it into the prepared pan.
Use a small piece of lightly buttered parchment paper to gently press the cereal into the pan and corners, smoothing the top. Optional step: Randomly place extra marshmallows on top of the squares for brighter colours. Cool the treats in the refrigerator for 30 minutes before slicing and serving.
Notes
Large marshmallows can be used but take longer to melt than mini marshmallows.
Clear vanilla will keep your melted marshmallows more white than standard brown vanilla.
This recipe makes a very gooey marshmallow treat. If you like a higher ratio of cereal, add an extra cup of Lucky Charms (42 grams).
The marshmallows will hydrate slightly as the bars sit, turning a more vibrant colour.