Traditional pudding uses either cornstarch or all purpose flour. For keto puddings, I like to use a bit of arrowroot powder and/or xanthan gum. Arrowroot is a great replacement for regular flour since it will thicken puddings and sauces with only 7 carbs per tablespoon. Make sure to lightly sprinkle it in at the end of cooking to avoid it getting gummy. I use xanthan gum the same way but in a much smaller quantity, only about 1/2-1 teaspoon is needed.