Preheat oven to 175 C, 10 minutes before baking. Line a standard 12-cup muffin pans with paper cups. Into the bowl of an electric mixer, sift together ingredients listed from plain flour - salt. Add sugar to that and give it a stir. Attach bowl to mixer fitted with the paddle attachment; add the ingredients listed from eggs -warm water. Beat on low speed until smooth and combined, about 3 minutes; scrape down the sides of the bowl as needed.
Divide the batter evenly among the muffin cups, filling each about two-thirds full. Bake in the preheated oven, until a skewer inserted in the center of the cupcake comes out clean, around 20-25 mins. Let them cool completely before frosting.
To make icing:
Melt butter. Stir in cocoa. Alternately add powdered sugar and milk, beating to spreading consistency. Add small amount additional milk, if needed. Stir in vanilla. This qty gives about 2 cups icing.
Notes
I only made half of the cupcake & icing qty mentioned above. I got 15 cupcakes. I used Hershey's cocoa powder for both the cake & icing. It was the regular cocoa powder & not dutch processed. You can also mix the batter using a hand blender. I poured around 3 tbsp batter in each muffin case. My cupcakes were ready in 20 mins. You can store it in the refrigerator for 3-4 days. You can also make this as a layered cake or sheet cake.For a layered cake, use two 8 inch round cake pans and bake for about 40-45 mins. (as given in the Martha Stewart's Baking handbook)For a sheet cake, use 13-by-9 inch pan and bake for 45-50 mins. (as given in the Martha Stewart's Baking handbook)