Grease a large mixing bowl. Pour the Rice Krispies Cereal into the bowl. Begin to melt the butter in a saucepan set over low heat. Add the marshmallows and stir to coat. Continue to heat the marshmallows, stirring occasionally, until about ¾’s of them are melted. Then remove the pan from the heat, and continue to stir, smashing the marshmallows, until they have all melted. Stir in the peppermint extract and green food coloring. Pour the melted marshmallows over the cereal and toss to coat. Let the mixture cool for 5-8 minutes. Reserve about 3 tablespoons of the mini chocolate chips for on top then toss the rest into the cereal. Stir until combined then spread the mixture into a well-buttered 8-inch pan. Sprinkle the reserved mini chocolate chips over top. Allow the treats to cool at room temperature for at least 30 minutes. Remove the treats from the pan and cut into 16 squares.