Line a 9-inch (22 cm) square pan with 2 sheets of parchment paper and sprinkle the sugar over the bottom of the pan.
Chop the chocolate candy into small pieces, then transfer to the freezer while you prepare the crispy treat mixture.
In a large nonstick pot, melt the butter over medium-low heat. Reduce the heat to low, then add the marshmallows and stir until completely melted. Add the vanilla and stir to incorporate.
Stir in the rice cereal. Remove from heat. Let cool slightly.
Transfer half of the mixture to the prepared pan and press into an even layer. Add 2 cups (350 g) of the candy in an even layer, then top with the remaining rice cereal mixture and spread in an even layer. Top with the remaining candy.
Let set at room temperature for 2 hours, or in the refrigerator for 1 hour. Cut into 9 bars, then serve.