Whisk the egg in a medium bowl. Whisk the milk, 1/3 cup malted milk powder and the cornstarch in a medium saucepan until smooth. Bring to a simmer over medium heat, whisking, until slightly thickened, about 4 minutes (the mixture will look like heavy cream). Remove from the heat and whisk about 1/2 cup of the hot milk mixture into the beaten egg, then whisk the egg mixture into the remaining milk in the pan. Cook over medium heat, whisking, until thickened, about 2 minutes (the whisk should leave a thick trail when dragged). Remove from the heat. Add the chopped chocolate and vanilla and whisk until smooth.
Divide the pudding among 4 ramekins or small bowls. Place a piece of plastic wrap directly on the surface of each and refrigerate until set, at least 4 hours or overnight.
Whisk the heavy cream with the remaining 1 tablespoon malted milk powder in a medium bowl until soft peaks form. Top the pudding with the whipped cream and malted milk balls.