In a large microwave-safe bowl, whisk together milk, sugar, cornflour, and cocoa powder. Make sure there are no dry pockets of flour or cocoa powder — a smooth mixture will give you the best texture.
Place the bowl in the microwave and heat on high power for 3 minutes. Take it out, give it a good whisk, after every 30 seconds making sure to scrape the sides and bottom well to prevent lumps.
The mixture should thicken into a smooth, custard-like consistency that coats the back of a spoon. If it’s still too runny, continue microwaving in 15-second bursts until you reach the right thickness.
Immediately pour the hot pudding into greased ramekins or small bowls. Tap gently to remove any air bubbles and smooth out the top if needed.
Refrigerate for at least 4 hours, or preferably overnight, until fully set.
Once set, run a knife gently around the edges and invert onto a plate. If you prefer, you can skip unmoulding and serve directly in the ramekins.
Recipe by Bake with Shivesh at https://bakewithshivesh.com/chocolate-pudding-in-a-microwave/