With an electric mixer beat 200g butter and 400g sugar together, adding oil at you go. Add eggs one at a time, making sure they are fully incorporated before moving on to next one. Add vanilla.
Sift in the flour, cocoa, bicarb, baking powder, salt and instant coffee, and fold carefully.
Place into two 20cm (8 in) round tin sprayed with non stick spray, the bottom lined with baking parchment.
Bake in the preheated oven for 25 to 30 minutes, checking with a knife or skewer to test doneness.
While cake is baking prepare icing: Place condensed milk in a microwave safe bowl on high for 1 to 2 minutes until HOT. Add chocolate (do not stir). Let sit for 5 minutes before adding butter and gently folding till a uniform mixture is formed. Cover and set aside.
Once cake is out of the oven turn onto a wire rack to cool.
After 30 minutes the icing should be cooled enough to whip. Beat on high for 5 minutes, this incorporates air for a better texture. Refrigerate.
The cakes should now be cool enough to cut in half horizontally or 3 parts if you're feeling brave. Allow to cool fully - another 30 minutes or so.
Once the hour cooling time is up take the icing back out of the fridge and whip again for 5 minutes, this should now be fluffy and thick.
Place 1/2 the icing between the layers and the rest on top. Smooth from the middle out down the sides of the cake. Smooth with a flat knife placed intermittently in HOT water. This will ensure a smooth finish. Cake is now good to go, I recommend an overnight in the fridge before serving.
I like to moisten the cake with jam before layering up to frost. I tend to use cherry for milk or dark chocolate icing, and raspberry for white chocolate. Another great alternative is a white cake variation - leave out the coffee and cocoa - add in an extra 30g flour. Use lemon curd between the layers and frost with white chocolate fudge frosting - yum.