Add all but ¼ cup of the 2 cups of alternative milk to a small saucepan. Add your cornstarch to the leftover ¼ milk and mix until smooth.  Once smooth, add it to the rest of the milk, then add your sugar and salt.

Bring heat to medium and continue mixing with a spatula until thickened.  This can take up to 20 minutes. Remove from heat. Let sit for 20 minutes, then store in the fridge.