Prepare the pan: Spray a 9x13 pan with baking spray, line with parchment paper, and spray the paper. Set aside.
Heat a large, heavy-bottomed pot over medium-low heat. Add the butter and heat until melted. To brown butter, continue heating the butter until it turns golden brown and brown bits form on the bottom of the pan. This will take approx. 5-7 minutes.
Stir in 1 ½ bags of mini marshmallows. Stir until completely melted. Add the maple extract. Then stir in cereal. When the cereal is evenly coated with the marshmallow mixture, fold in the remaining marshmallows.
Transfer the cereal mixture to the prepared pan. Spray hands with baking spray and press the mixture evenly into the pan. Set aside to cool and set, approx. 60 minutes.
Using the parchment paper, lift the bars out of the pan. Slice into squares. Store in an airtight container for up to 3 days with parchment paper in between the layers.
For traditional treats, melt the butter but skip the browning step and proceed with instructions, omitting the maple extract.
Using a silicone spoon or spatula will reduce sticking with the marshmallow mixture.