I started making this as a child. My mother didn't keep treats in the house but she always encouraged me to make food and she taught me this one early on. To me, real chocolate pudding is a flash to my childhood, a warm hug, a feeling of safety.
It can be made either in the microwave or on the stove top. And, while it is quick to come together, it takes time to set up and cool down so plan for that.
Whisk all the ingredients in a microwave-safe bowl that is bigger than you need (the pudding will climb the sides of the bowl as it cooks). The cocoa will resist incorporating, but it will eventually.
Put in the microwave for 2 minutes on high. Take the bowl out and scrape the sides and whisk a bit to incorporate everything and make sure you have a smooth mix. Put it back in the microwave for another 2 minutes on high.
Stir and put back in for a final 2 minutes.
Whisk all the ingredients in a medium sized pot, preferably with a heavy bottom. Cook over medium heat, whisking or stirring most of the time so that the pudding doesn't stick and burn to the bottom or the sides of the pan. When the mixture starts to thicken and get glossy, remove from heat and pour into a serving dish/dishes. Let cool a bit and then refrigerate until fully set.
If you don't like a skin forming on the top of your pudding, wait until it has cooled a bit and then place a sheet of plastic wrap directly on the surface of the pudding, pushing out any air bubbles. Refrigerate.