Coat bottom and sides of an 8-inch pie plate lightly with butter.

Combine chocolate syrup and chocolate chips in a small microwave-safe bowl. Microwave on high until hot, about 45 seconds. Stir until smooth. Reserve 1/4 cup of the chocolate mixture.

Combine remaining chocolate mixture and cereal in a medium bowl and mix to coat cereal. Press mixture over bottom and up sides of prepared pie plate. Freeze until firm, about 15 minutes.

Combine reserved chocolate mixture and the sour cream in a small bowl and mix well. Spread half the ice cream in the prepared pie plate. Drizzle with half the sour cream mixture. Top with remaining ice cream and drizzle with remaining sour cream mixture. Freeze pie, covered, until firm, about 1 hour.