In a Dutch oven, combine marshmallows and butter. Cook and stir over medium-low heat until melted. Remove from the heat; stir in the cereal, 3/4 cup malt powder and 2-1/2 cups malted milk balls. Press into a greased 13x9-in. pan.
In a microwave-safe bowl, melt chocolate chips; stir until smooth. Stir in remaining malt powder. Spread over cereal bars. Sprinkle with remaining malted milk balls; press into chocolate. Let stand until set. Using a serrated knife, cut into squares.