In a large, heat-proof glass or steel mixing bowl, whisk together the syrup or sugar, eggs and coconut milk until well-combined. Add in about half the sliced bananas. Place the bowl over a saucepan with about 1" of simmering water (to create a make-shift double boiler).
Heat the coconut milk mixture in the double boiler until very hot, stirring frequently to prevent scorching. Meanwhile, in a small bowl, whisk together the cornstarch and water. Once the coconut milk mixture is hot, whisk in the cornstarch mixture and continue stirring mixture until pudding thickens to the consistency of thin yogurt. The added bananas will break down as it cooks.
Remove from heat, stir in the vanilla extra and salt. Set aside to cool for a few minutes before assembling the pudding.
To assemble, layer ⅓ of the vanilla wafers and ⅓ of the remaining banana slices on the bottom of a trifle dish or bowl. Top with half of the pudding. Then repeat the layers ending with the last of the wafers and banana slices. Refrigerate for 3-4 hours or until completely cooled through. Serve with sweetened whipped cream and shredded coconut for topping.