Melt chocolate and butter in a microwave-safe bowl in 30-second intervals, stirring after each melting, for 1 to 3 minutes (depending on your microwave). Stir in rice cereal.
Spread cereal mixture into prepared pie dish, pressing cereal down to make a crust. Freeze crust until firm, about 15 minutes. Spread softened ice cream evenly over crust; freeze until ready to serve.