In a medium heavy bottom saucepan, whisk together the coconut milk, brown sugar, and cocoa powder. Bring to a rolling boil over medium heat, then remove from heat. Stir in the chopped semisweet chocolate and the vanilla, let sit for a minute and then whisk very well to melt the chocolate.
Place mixture in the refrigerator until very cold, or preferably over night.
When ready to make the ice cream, remove the base from the fridge. In a small bowl, whisk the maple syrup into the peanut butter. Then place the base in an ice cream maker and make it according to your ice cream maker's instructions. When ice cream is about halfway churned, drizzle in the peanut butter mixture. Place in the freezer and freeze until firm.