Preheat oven to 350F. Grease the bottom and sides of an 8-inch cake pan with parchment paper. Set aside.
In a large bowl, mix the flour, sugar, baking powder, baking soda and salt.
In a bowl of standing mixer with a paddle attachment, mix coconut milk, egg, oil, vanilla and vinegar on medium speed until well combined.
Reduce the speed to low and slowly add the dry ingredients. Mix until just incorporated.
Pour the batter into the prepared pan and smooth the top.
Bake 18 to 20 minutes or until a toothpick inserted into the cake comes out clean.
Remove the cake from the oven and let cool completely.
To prepare coconut mousse, sprinkle gelatin over the water in a small bowl, let stand for 5 minutes.
In a saucepan, warm coconut milk, sugar and shredded coconuts over medium-low heat until sugar is dissolved. Stir in gelatin mixture to dissolve. Remove from heat. Strain mixture through a fine-mesh sieve into a clean bowl. Let cool completely.
Whip the heavy cream until it becomes stiff. Add the cream to the cooled coconut mixture and fold with a spatula until it becomes one liquid.
To assemble, line the bottom and sides of an 8-inch springform pan with parchment paper.
Place in the coconut cake layer. Then pour the coconut mousse mixture over the cake. Juggle to lightly level the top.
Chill in the refrigerator overnight.
To prepare meringue, combine sugar and egg whites in a large heatproof bowl. Using a handheld electric mixer, beat on high speed until foamy for a minute. Set bowl over a pan of barely simmering water. Beat on high speed until the mixture is hot to touch. Remove from heat, continue beating meringue until it becomes stiff and glossy.
Remove cake from the refrigerator. Transfer cake from cake pan to a serving plate. Peel off the parchment papers.
Pipe or smear the meringue on top of the cake. Using a kitchen torch, lightly brown the meringue. Sprinkle toasted coconut on top.