Preheat oven to 180°C (350°F). Line 2 muffin trays cups with cupcake liners. Set aside.
In a large bowl whisk together sugar, flour, cocoa powder, baking powder, baking soda and salt.
Add vegetable oil and milk. Stir well, until combined.Add the eggs, one at a time and stirring well after each addition.Add vanilla extract.
Add hot water and stir until the mixture is well combined and there are no lumps.The batter will be very thin and runny. It is the way it should be. Nothing to worry about.
With a deep spoon or a scoop fill the prepared cupcake cups with batter, just 2/3 of the way. Do not overfill, otherwise the cupcakes might sink in the middle. Just make extra cupcakes with the leftover batter, or just discard it.
Bake the cupcake for 18-22 minutes, or until a toothpick inserted in the center of a cupcake comes out clean.
Take the cupcakes out of the oven and allow to cool for a couple of minutes in the pan, before transferring to a wire rack, to cool completely.
To prepare the Swiss Meringue Frosting:
Bring ½ cup of water to boil in a medium saucepan. Once boiling, turn down the heat, but keep at a simmer.
In a heat proof metal bowl, whisk together the egg whites, sugar and cream of tartar/vinegar.Place over the saucepan with simmering water. Make sure the bottom of the bowl is not touching the water.Constantly whisking, cook until the mixture feels war to the touch and the sugar has completely dissolved. You can check by rubbing the mixture between your fingers, it should not feel grainy and should be warm.
Remove from heat and transfer to a bowl of a stand mixer, or mix with a hand mixer.
Beat on high speed until stiff peaks form. It will take about 10 minutes. The cream will be glossy and smooth.
Add the vanilla extract and mix through to incorporate.
Fill a piping bag with the frosting and top the cooled down cupcakes. You can also food coloring to the frosting, if desired.
Notes
Raw eggs should not be used when serving food for pregnant women.