Step 1
Preheat oven to 350 degrees F (175 degrees C).
Step 2
Grease a 10-inch round cake pan and dust with unsweetened cocoa powder.
Step 3
Stir cake mix 1 1/4 cup water vegetable oil and eggs in a large bowl until moistened. Beat with an electric mixer on medium speed until batter is smooth 2 minutes.
Step 4
Pour batter into the prepared cake pan.
Step 5
Bake in preheated oven until the cake top springs back when lightly pressed and a toothpick inserted into the middle of the cake comes out clean 30 to 35 minutes.
Step 6
Place a stainless steel bowl and beaters in refrigerator until chilled at least 20 minutes.
Step 7
Cool the cake in the pan on a wire rack for 15 minutes before removing to finish cooling completely.
Step 8
Place unsweetened baking chocolate into a microwave-safe bowl and heat in microwave on high power until chocolate is slightly warmed about 1 minute. Continue to heat chocolate in 20-second intervals stirring after each interval until chocolate is melted and free of lumps.
Step 9
Stir melted chocolate with sweetened condensed milk in a large bowl until thoroughly combined; whisk in 1/4 cup water and instant chocolate pudding mix until thickened and smooth about 1 minute. Cover bowl and chill pudding mixture until cold at least 30 minutes.
Step 9
Whip cream in the chilled stainless steel bowl with chilled beaters until the cream holds stiff peaks about 2 minutes. If necessary use a cloth to touch the steel bowl to avoid warming the bowl.