Line two 9x9x2-inch baking pans with parchment paper. Greast pans; set aside.
In a medium mixing bowl stir together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
Preheat oven to 350 degrees F. In a large mixing bowl beat the butter with electric mixer on medium-high for 30 seconds. Add sugar; beat until combined. Add eggs, one at a time, beating 30 seconds after each. Beat in chocolate and vanilla. Alternately add flour mixture and milk, beating on low after each addition until thoroughly combined.
Divide batter between prepared pans; spread evenly. Bake for 10 to 15 minutes. Sprinkle with malted milk balls, pressing in slightly if needed (see Tip below). Continue baking 10 to 15 minutes more (25 minutes total baking time).
Let cakes stand on wire racks while preparing Chocolate Malt Glaze. Spread warm cake with warm glaze.
Keep it Crunchy
For the candy to keep its shape and crunch, partially bake the cakes until nearly set. Press in the chopped balls, then continue baking for the remaining time.
Chocolate Malt Glaze
In a medium microwave-safe bowl, whisk together whipping cream and malted milk powder. Microwave on 50% power (medium) for 2 minutes or until bubbly.
Place chocolate pieces in another medium heat-proof bowl; pour hot whipping cream mixture over chocolate pieces. Let stand 5 minutes; stir until smooth.