Although almond milk seems like it should be a modern, industrial product, made for vegans and those with food allergies, it actually has a lengthy history. It was widely used in the Middle Ages as a milk substitute, partly as a workaround for fasts that forbade animal products and partly because dairy milk was more valuable as cheese. Almond milk puddings, known by the French name "blancmange" or the Italian "biancomangiare," were considered an especially elegant dish.
You might not opt to make your own almond milk by hand-grinding the almonds, as they did in those days, but you can certainly make a perfectly good pudding either from a mix or from scratch.
Jell-O Pudding With Almond Milk
You may have had the experience of trying to make an instant pudding mix with nondairy milk, instead of dairy milk, and had it fail to thicken. The problem is that the instructions on Jell-O instant pudding, and most other brands, call for full-fat milk. This is a much richer fluid than almond milk, and requires less thickening.
With a cooked pudding mix, you could simply add more starch, but that won't work with the instant variety. Instead, the trick is to cut back on the quantity of nondairy milk you use. Instead of the 2 cups of regular milk that the instructions call for, start with 1 cup and add more a tablespoon or two at a time until you reach the right consistency, which should fall somewhere between 1 1/4 and 1 1/3 cups.
Homemade almond milk is slightly thinner than the commercial kind, which has a few additives to give it a more milk-like mouth feel, so you'll use a bit less with homemade and a bit more with commercial almond milk.
Pudding With Almond Milk Recipe
You can't make your own "instant" pudding with almond milk and cornstarch, because commercial instant puddings are carefully formulated to thicken at room temperature. Ordinary starches, like cornstarch or arrowroot, require heat and cooking before they can thicken.
The good news is that starch-thickened puddings are still very simple and easy to make, and require minimal cooking time. The key thing with any recipe is the ratio of starch to liquid. With cornstarch, you'll need about 4 teaspoons to thicken a cup of alternative milk. Three teaspoons make up 1 tablespoon, and there are 2 tablespoons in every fluid ounce, so once you've mastered that ratio, you can do the math to make whatever size batch makes sense for you.
Suppose you wanted to make a pudding using 3 cups of almond milk. That's a half-cup serving each for six people, which is pretty reasonable. Three cups at 4 teaspoons per cup gives you 12 teaspoons, which is 4 tablespoons, which is 1/4 cup. So you'd whisk 1/4 cup of cornstarch into your 3 cups of milk, along with the other ingredients, to get a workable pudding.
Again, you may need to use slightly more or less depending whether the almond milk is homemade or commercial. If you avoid grains, you can use root-derived arrowroot or tapioca starch instead of cornstarch, in roughly the same ratio. Arrowroot is the better choice, because if it's your sole thickener, tapioca can give the finished pudding an odd texture that some find unpleasant.
Molded Almond Milk Pudding
If you'd like to go totally old-school, you can even make a modern version of blancmange or biancomangiare. These use more starch relative to the amount of milk, roughly 1/2 cup of starch to a quart of almond milk. This makes the finished pudding firm enough to unmold once it's set, somewhat like a panna cotta.
Most modern recipes are flavored with vanilla, but some use orange blossom water or rose water as a nod to their Mediterranean heritage. Either way, the finished pudding is elegant and understated, and looks very pretty with a colorful, fruit-based sauce.