To toast the coconut, spread the coconut onto a rimmed sheet pan. Toast in a 350°F oven, stirring frequently, until the coconut is an even brown color, about 10 minutes. Set aside to cool.
Butter an 9×13-inch baking pan. Line the baking pan with parchment paper letting the paper extend up the two short sides of the pan and overhang slightly on both ends. Butter paper; set pan aside.
In a large saucepan over low heat, melt butter. Add marshmallows and stir frequently until melted, about 6 minutes. Stir in shredded coconut and coconut extract. Remove from heat and stir in rice cereal. Using a piece of wax paper, press rice mixture evenly into prepared pan. Sprinkle with toasted coconut and press lightly to adhere to the top of the treats.
In a small, microwave safe bowl, heat the chocolate in the microwave on high for 30 seconds. Stir, and return to microwave, heating in 15 second intervals and stirring well between each heating, until chocolate is melted. Drizzle melted chocolate over the treats in the pan.
Cool at room temperature until chocolate hardens. Cut into squares.