Open the coconut milk and stir to combine if separated. Set aside ½ cup milk.
Pour the remaining coconut milk into a saucepan. Add ½ cup agave syrup / maple syrup / honey / cane sugar and ¼ tsp salt.
Warm the milk on the stove over medium-low heat, stirring occasionally, until the sweetener has completely dissolved into the coconut milk (1-2m).
Measure the cornstarch and add it to the reserved 1/2 cup coconut milk. Whisk thoroughly until the cornstarch is totally dissolved.
Pour the cornstarch mixture into the warm coconut milk while whisking gently.
This is your ice cream base. Increase the heat to medium. Stirring occasionally, continue cooking the base until it has thickened enough to coat the back of a spoon, 6 to 8 minutes. Do not allow the base come to a boil.
Remove the base from heat and stir in the vanilla.
Pour the base into a shallow container. Let the base cool slightly on the counter so it's not hot when you put it in the fridge. Before refrigerating, press a piece of plastic wrap against the surface — this coconut milk base doesn't form a skin quite as badly as a milk-and-egg base, but it doesn't hurt! Cover the container and refrigerate for at least 4 hours or for up to 3 days.
Remove the base from the fridge. It should be completely chilled and slightly pudding-like in texture. Pour the base into your ice cream machine and begin churning.
Churn the ice cream until it thickens considerably and is roughly the consistency of soft-serve ice cream. Depending on your machine, this could take anywhere from 10 to 20 minutes — keep an eye on it! If you want to add any extras, add them now and churn a few more seconds until they are fully incorporated.
Scrape the ice cream into your freezer container. Press a piece of parchment or wax paper against the surface to prevent ice crystals from forming.
Transfer the container of ice cream to the freezer and freeze for at least 4 hours to harden the ice cream.
From The Kitchn