In a large mixing bowl, add the following ingredients one at a time, beating well after each addition: eggs, caster sugar, butter, oil, cocoa, buttermilk and vanilla essence.
Sift the flour, baking powder, bicarbonate of soda and salt; add to the sugar and egg mixture. Blend well and fold in the boiling water.
Spoon the mixture in two greased and floured 20cm round cake pans. Divide the chocolate chips in half and sprinkle them over each pan. Bake in preheated oven for 25 minutes. Cool.
To make the Chocolate icing: Begin by beating together, butter, icing sugar and cocoa. Add vanilla essence milk and coffee. Beat until very smooth. Add more icing sugar until you obtain the consistency you want. Spread on cooled cake.