Line an 8x8 inch baking pan with parchment paper and set to the side.
Melt the butter in a large saucepan over medium-low heat. Allow the butter to brown, until small brown flakes appear at the bottom. Add the marshmallows, salt and vanilla and stir until melted - about 3 minutes. Turn the heat off.
Pour the marshmallows over the cereal and use a rubber spatula to stir together, evenly covering the cereal. Work quickly as the marshmallow will begin to set!
Stir in the mini m&ms, do this gently as you don't want the color to bleed.
Pour the cereal into your prepared pan. Use an offset spatula or rubber spatula to gently press down and make the top even. You can sprinkle over extra mini m&m's if you wish.
Place in the fridge for one hour, then cut into 16 squares.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. Marshmallows: you can use regular sized marshmallows or mini marshmallows. Looking for a recipe with marshmallow fluff? Check out this recipe and just add m&ms! m&ms: I've used mini m&m's here which you can get at Target or the grocery store, but you can use regular m&Ms or seasonal ones! Storage: slice the treats into 16 bars and keep in an air tight container for up to 5 days. I do not recommend freezing these as it will alter the texture.