Preheat oven to 350 degrees and line muffin tin with paper liners.
Sift the flour, cocoa powder, salt, baking soda and baking powder together in a large bowl.
Whisk in the egg, milk, oil and vanilla.
Heat the 1/2 cup of water in a glass measuring cup in the microwave for about 1-2 minutes until boiling. Whisk into batter until combined and smooth. Batter will be thin.
Fill cupcake liners until 2/3 full. Do not overfill. Bake for 20-22 minutes or until a tooth pick comes out clean. Take out of the muffin tin cook on a wire rack.
Using a mixer beat the cream cheese until smooth and fluffy. Add in the butter a couple of tablespoons at a time and beat until combined.
Add the powdered sugar and cocoa powder mixture and vanilla extract all at once and mix frosting until smooth and combined.
Spread of pipe on cooled cupcakes. Store leftover frosting in the fridge in an air-tight container.