Preheat oven to 350°.
Coat bottoms of 2 (9-inch) round cake pans with cooking spray (do not coat sides of pan); line bottoms with wax paper. Coat wax paper with cooking spray; dust with 1 tablespoon flour.
Combine butter, vanilla, and cream cheese in a large bowl; beat at medium-high speed of a mixer 2 minutes. Gradually add sugar, beating at low speed just until smooth. Add hot water; beat just until smooth. Add chocolate; beat just until smooth. Reserve 1 3/4 cups chocolate mixture for frosting; cover and chill 2 hours. Add shortening to remaining chocolate mixture in bowl. Beat at medium speed of a mixer until well-blended (about 1 minute). Add eggs, 1 at a time, beating well after each addition.
Lightly spoon 1 3/4 cups flour into dry measuring cups, level with a knife. Combine 1 3/4 cups flour, milk powder, baking powder, and salt, stirring well with a whisk. Add the flour mixture to the egg mixture alternately with milk, beginning and ending with the flour mixture.
Pour batter into prepared pans. Sharply tap pans once on counter to remove air bubbles. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes on a wire rack; remove from pans. Remove wax paper. Cool completely on wire rack.
Place 1 cake layer on a plate; spread with 1/2 cup frosting, and top with remaining cake layer. Spread remaining frosting over top and sides of cake; sprinkle top of cake with chopped malted-milk balls. Chill 1 hour. Store cake loosely covered in refrigerator.