Preheat oven to 325 F.
Grease and flour a 9 x 13 baking pan. Set aside.
In a large bowl cream together butter, oil, brown sugar, and white sugar.
Mix in eggs and vanilla extract.
Mix in unsweetened cocoa powder.
Mix in buttermilk and plain hot coffee until all ingredients are well incorporated.
Add in flour.
Sprinkle in salt, baking powder and baking soda.
Mix until batter is smooth.
Pour batter in prepared pan and smooth out.
Bake for 30-35 minutes or until moist crumbs cling to a toothpick inserted into the center.
To prepare the filling (while cake is baking) add sweetened condensed milk and chocolate chips into a microwave safe bowl.
Stir and microwave in 10 second intervals until chocolate is melted. Set aside.
When cake comes out of the oven, poke small holes all over the cake about an inch apart.
Pour the chocolate filling all over cake.
Let cake cool completely. (I place it in the fridge)
To make the whipped topping, add heavy cream in a medium bowl.
Mix until cream begins to thicken and fluff.
Do not over mix, once cream is fluffy, stop mixing.
Stir in unsweetened cocoa powder and powdered sugar until smooth.
Fold in vanilla extract.
Spread whipped topping over cooled cake.
Sprinkle with mini chocolate chips.
Refrigerate until whipped topping is firm (I normally skip this step and dig right in)
Store cake in the refrigerator.