In a medium size bowl (I use a 1.5 liter Pyrex), whisk together the tapioca starch and almond or oat milk.
Pour the can of coconut milk into a small to medium (2 quart) saucepan. Whisk in the sugar, maple syrup, and cocoa powder, then whisk in the dissolved tapioca & milk mixture.
Turn heat to medium and cook, whisking constantly,until mixture comes to a gentle boil. Continue to boil and whisk for about a minute (especially if using cornstarch). Mixture should thicken just slighty. Remove from heat and pour back into the bowl you used for whisking together the starch & milk.
Let cool for about 5 minutes, then whisk in the vanilla extract. Spray a small sheet of parchment with cooking spray and press it over the custard base. You can use olive oil spray or a lecithin spray like Pam.
Let cool at room temperature until it's cool enough that you feel comfortable with putting it in the refrigerator, then cover and chill for 4 hours or until very cold.
Process the mixture in your ice cream maker as directed by manufacturer.