Preheat oven to 350°F Grease 13 x 9-inch baking pan. Line pan with foil; grease foil.
Prepare Chocolate Base: In a heavy 3-quart saucepan, melt margarine or butter with chocolates over low heat, stirring frequently. Remove saucepan from heat. With a wooden spoon, stir in sugar and vanilla, then stir in eggs until well mixed.
In a small bowl, combine flour, baking powder and salt; stir into chocolate mixture just until blended.
Spread batter evenly in pan. Bake 25 to 30 minutes, until toothpick inserted 1-inch from edge comes out clean. Remove pan from oven. Cool completely in pan on wire rack.
Prepare Malted-Milk Topping: In a small bowl, mix malted-milk powder, milk and vanilla until blended. Stir in margarine or butter, then confectioners' sugar, until blended. Spread topping over cooled bars; top with chopped malted-milk-ball candies.
When topping is firm, transfer with foil to cutting board. Cut lengthwise into 4 strips, then cut each strip crosswise into 8 pieces.