To make the mousse. In a microwave safe bowl add the chocolate. Microwave on 30 second intervals, stirring after each, until melted and smooth. Stir in the melted butter, it will thicken. Set aside to cool.
In a small saucepan whisk together the egg yolks, 2 tablespoons water and sugar. Place on the stove over medium heat and stir constantly until the sauce thickens slightly and just coats the back of a spoon, about 2-3 minutes. Make sure to remove the eggs from the stove the minute they begin to curdle and thicken. Stir the melted chocolate into the egg mixture until completely smooth. Place in the fridge while you whip the cream. Place the cream in the bowl of a stand mixer (or a large bowl using a hand mixer) and whip cream until stiff peaks form. Add the vanilla and coconut rum (if using) and whip until combined. Make sure not to over-beat, cream will then become lumpy and butter-like. Now add half the whipped cream with cooled chocolate mixture. Gently fold the cream into the chocolate until no more streaks remain. Add the remaining cream and gently fold into the mousse. Cover the bowl and place in the fridge for two hours or overnight.
To make the coconut rum cream. In a medium saucepan combine the coconut milk and cornstarch. Whisk until the cornstarch is completely dissolved and there are no lumps. Add the sugar, eggs and salt, whisk until smooth. Place the pan on the stove and bring to a boil, stirring constantly. Simmer until the cream thickens and is smooth like pudding, about 5 minutes. Remove from the heat and stir in the vanilla, coconut rum (if using) and shredded coconut. Transfer the cream to a bowl, cover and chill two hours or overnight.
To make the crepes. Add butter to a small saucepan and heat over medium heat. Whisk constantly until brown bits appear on the bottom, about 5-6 minutes, then immediately remove from heat and set aside. Combine the eggs, milk, flour, the melted + browned butter, salt, 1 cup water and vanilla in a blender or food processor. Pulse for 30 seconds or until well combined. Place the crepe batter in the refrigerator for about 30 minutes or overnight. This allows the bubbles to subside so the crepes will be less likely to tear during cooking. The batter will keep for up to 48 hours.
Remove the batter from the fridge and whisk in the remaining 1/4 cup water. Heat a 10 to 12 inch (I used a 10 inch) non-stick skillet or cast iron skillet over low-medium heat (never go above medium low). Add cooking spray (I think cooking spray works best) to coat. In a circular motion pour 1/4 cup of batter (I measure it out for every single crepe) into the skillet. Quickly pick the skillet up (using an oven mitt, especially if using a cast iron skillet!) and swirl in a circular motion to spread evenly. Cook for 30 seconds and flip. Cook for another 10 seconds and remove to a cutting board. Lay them out flat so they can cool on a piece of parchment paper. After 5 minutes or so I like to flip the crepes to make sure they are not sticking to the parchment. Continue until all batter is gone. Makes 20 crepes.
To assemble the cake. Place the bowl of a stand mixer (or a large bowl) and your whisk attachment (or beaters) in the freezer.
Lay all 20 crepes (or however many you made, but I think you need at least 15. I had 19) out on a large clean counter. Remove the chocolate mouse and coconut cream from the fridge and evenly divide both the mouse and coconut cream among all 20 crepes (10 with chocolate mousse, 10 with coconut cream) and spread in an even, thin layer. Now place one crepe in the center of your serving plate and layer on the rest alternating between the chocolate mousse and coconut cream (one coconut cream layer, one chocolate mouse layer and so on). Do your best to try and keep the stack straight. Once you have used all the crepes and the cake is assembled place it in the fridge while you whip the coconut cream.
Flip your cold can of coconut milk upside down and open it. There should be around 1/2 cup of coconut water at the top. Pour this into a container and save for another use. Scoop out the coconut cream and place in a bowl. Whip the cream until soft peaks form. It will not be stiff like regular whipped cream Beat in the powdered sugar. Remove the cake from the fridge and top with your desired amount of coconut whipped cream. Place back in the fridge for 30 minutes or until ready to serve. When ready to serve, top the cake with toasted coconut, rum toasted pecans and a drizzle of chocolate ganache (below) if desired. Slice and eat!
To make the ganache combine 2 ounces chocolate and 2 tablespoons coconut milk in a small microwave safe bowl. Melt the chocolate in the microwave on 30 second intervals, stirring between each until the chocolate and coconut milk are smooth. Stir in 1 tablespoon coconut rum or vanilla extract.