Line a 9x9-inch baking pan with parchment paper.
In a large pot over low heat, melt the butter.
Add the mini marshmallows and stir until completely melted and smooth.
Stir in the ube extract until evenly incorporated and the mixture is a vibrant purple color.
Remove from heat and gently fold in the Rice Krispies until fully coated.
Transfer the mixture to the prepared pan and press it evenly into the corners using a spatula.
If desired, sprinkle extra mini marshmallows on top and gently press them into the surface.
Let cool at room temperature before slicing into 9 squares. Enjoy!