Add all except about 1/2 cup of the coconut milk to a small saucepan. To the pan, add the cocoa powder, maple syrup, vanilla and salt. Whisk together, turn the heat to medium and continue to whisk occasionally.
14 ounces (400 grams) full-fat canned coconut milk, 1/2 cup (55 grams) Dutch-process cocoa powder, 1/2 cup (160 grams) maple syrup, 2 teaspoons vanilla extract, 3/8 teaspoon salt
Meanwhile, mix the remaining 1/2 cup coconut milk with the arrowroot starch in a small bowl until well combined. It may appear lumpy at first but keep stirring and it'll combine.
1 1/2 tablespoons arrowroot starch/powder if using maple syrup or 1 tablespoon if using coconut sugar
As the mixture on the stove starts to get hot, whisk more frequently, making sure it doesn't burn or clump together on the bottom. Once it starts to bubble, whisk in the arrowroot and coconut mixture while stirring constantly. Whisking constantly now, cook until thickened. Do not walk away and do not stop whisking! This will take 1-10 minutes depending on how hot the mixture was before adding the arrowroot. Do not let it continue cooking more than one minute after it's thickened - this can cause the arrowroot to break down and will make the pudding runny. It'll thicken a little more once chilled.
Let cool until room temperature, stirring frequently so that a skin doesn't form, and then refrigerate in an airtight container. Refrigerate for up to 4 days.