Start by sifting your flour, baking powder, cocoa powder, instant coffee & salt into a large bowl then add the oil (or butter), sugar, egg yolks and heavy cream and mix it together thoroughly.

In your mixer bowl add the egg whites and cream of tarter and start the mixer. Beat it until it becomes fluffy by adding the sugar gradually. Beat it at low-medium speed.

Fold the batter into the mixer bowl. Line the pan with wax paper and pour the batter into the pan. Tap it a few times to release the large bubbles and bake it in the oven at 325 F degrees for 35-45 minutes. Check if it's done by sticking a toothpick in it.

Place it in a cooling rack and allow to cool before removing the pan. Meantime, mix your buttercream by adding the coffee into the evaporated milk. Place the room temperature butter in the mixer and mix until light and fluffy.

Slowly add the condensed milk. Continue to beat, then add the coffee mixture, vanilla, salt, and powdered sugar. Continue to beat until it makes a smooth buttercream. Transfer it in a bowl and set it aside.