Heat oven to 180 C (350 F). Grease and flour two 9-inch round baking pans.
In a stand mixer bowl, sift and mix together sugar, flour, cocoa, baking powder, baking soda and salt.
Add eggs, milk, vegetable oil and vanilla; mix mixture together for 2 minutes. On low speed, add in boiling water (batter will be thin). Pour batter into prepared pans.
Bake 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes, remove from pans to wire racks. Cool completely. Frost with chocolate frosting.
Baking variations:One pan cake: Grease and flour 13×9×2 inch pan. Heat oven to 180c (350 F). Pour batter into prepared pan. Bake 35 to 40 minutes. Cool completely. Frost.
Three layer cake: Grease and flour three 8-Inch round baking pans. Heat oven to 180c (350 F). Pour batter into prepared pans. Bake 25 to 30 minutes. Cool completely. Frost.
Cupcakes: Line muffin cups (2- 1/2 inches in diameter) with paper bake cups. Heat oven to 180c (350 F). Fill cups 2/3 full with batter. Bake 20 to 25 minutes. Cool completely. Frost about 24 cupcakes.
Icing:In a stand mixer bowl, mix butter until soften, add sifted cocoa powder and blitz until fully combined. Alternatively mix icing sugar and milk, and blitz until it becomes a spreadable consistency.
Add vanilla essence, and blitz for 30 seconds.
Spread the chocolate icing between layers of cake, over top and side of cake. Serve.