In a pot, combine sugar, cornstarch, and cocoa powder, until mixed. Add soy milk and mint extract, and stir briefly--don't worry about the lumps.
Place pot over medium heat and stir. And stir some more. As the liquid heats, the lumps should disappear. Make sure you stir thoroughly; there shouldn't be any clumps on the bottom or side of the pot.
Continue stirring until the pudding begins to thicken. This can take awhile, so be patient--it will thicken eventually, don't worry! When thickened, remove pan from burner to let cool.
Stir often while cooling or your pudding will develop a "skin" on top. Transfer to serving dishes or a storage container when desired, although it shouldn't still be quite hot. Store in refrigerator until pudding has set, then serve.