• Grease and line 2 - 6 inch cake pans or 1 - 7 or 8 inch pan. Preheat the oven to 350 F - 175 C for at least 15 mins.
• Sieve together flour, cocoa, salt, baking powder and baking soda to a mixing bowl. Stir in the sugar and mix until well combined.
• Make a well in the center of the bowl. Pour egg, oil, vanilla extract & milk. Whisk together all the wet ingredients. Then mix wet and dry together until just combined and no lumps appear.
• Pour boiling hot water and whisk until all the water is absorbed by the batter. The batter is runny at this stage. Pour this to the cake pans. Tap the pans gently twice to the counter. 
• Bake for 28 to 30 mins or until the tester inserted comes out clean. Please adjust the timing as it varies from oven to oven.
• Cool the cake in the pans on a wire rack for 10 mins. Invert to a cooling rack and cool completely before frosting.

Making chocolate buttercream frosting

• Ensure butter is soft yet cold. Beat it until light & creamy for  2 mins. Then add the rest of the ingredients except milk. Beat until smooth, light and creamy. If the frosting is too thick add milk and beat. If it becomes runny, just add more powdered sugar.
• Refrigerate for a while and spread on the cake. For more details watch the video. Refrigerate and use up the chocolate cake with in a week.