Whisk egg yolks and evaporated milk in a medium saucepan. Stir in sugars, salt, and vanilla.
Cook over medium heat, stirring frequently until mixture comes to a low boil. Continue cooking, stirring constantly, until mixture thickens to a pudding-like consistency (about 10mins).
Remove from heat. Add butter, coconut, and pecans and stir until combined. Cool completely before using on cake.
Chocolate Cake:
Preheat oven to 350F, grease three 8" round baking pans and dust with cocoa powder. Line bottoms with parchment.
Place all dry ingredients into the bowl of a stand mixer fitted with a paddle attachment. Stir to combine.
In a medium bowl whisk all wet ingredients (pour hot water in slowly as not to cook the eggs).
Add wet ingredients to dry and mix on medium for 2-3 mins. Batter will be very thin.
Pour evenly into prepared pans. I used a kitchen scale to ensure the batter is evenly distributed.
Bake for 30-35 mins or until a cake tester comes out mostly clean.
Cool 10 minutes in the pans then turn out onto a wire rack to cool completely.
Chocolate Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a pot with about 1" of simmering water. Whisk constantly until the mixture is hot and no longer grainy to the touch (about 3mins). Or registers 160F on a candy thermometer.
Place bowl on your stand mixer and whip on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.**
Add cooled melted chocolate, cocoa powder, and vanilla. Whip until smooth.
Assembly:
Place a layer of cake on a cake board or plate. Spread a thin layer of buttercream on top of the layer (optional) and pipe a border around the outside to hold the filling in. Fill with about 3/4 cup of coconut pecan filling. Repeat with next layer.
Place final layer on top and do a thin crumb coat on the cake. Chill for 20mins.
Frost the top and sides of the cake with remaining frosting. Do a decorative border on top using a 6B tip if desired. Chill for 30mins.
Fill top center with remaining coconut pecan filling and spread evenly. Sprinkle with toasted coconut and chopped pecans. Press toasted coconut and pecans along the bottom if desired.
Notes
* Wipe your mixer bowl and whisk down with lemon juice or vinegar to make sure it is completely grease free and make sure there is no trace of yolk in your whites or your meringue will not stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. If it looks soupy, place it in the fridge for 20mins and rewhip.