In a bowl, mix together the corn starch and cold water into a slurry and set aside. You'll use this later to thicken the pudding.
Whisk together the almond milk, sugar, cocoa powder, and vanilla in your sauce pan. It might look bubbly, but that's fine.
Whisk in the cornstarch mixture, and put the saucepan over medium-high heat.
Stir often as the pudding heats, and whisk constantly as it thickens.
Once thickened, about 5-8 minutes, remove from the heat. You can cool this quickly by immersing the bottom of the pan in a bowl of cold water and continuing to stir, or you can just let it cool normally. Make sure to stir occasionally to avoid letting a film form on top.
Once cooled, transfer your pudding to a serving dish, cover with plastic wrap, and chill until you're ready to enjoy. Top with your favorite toppings, or don't, and eat!