Heat oven to 350F. Butter two 9-inch round cake pans and line bottoms with parchment. Melt the chocolate with water in a small saucepan over low heat, stirring until smooth. Set aside to cool slightly.

Whisk flour, baking soda, and salt in a medium bowl. In a large bowl, beat butter and sugar on medium-high until light and fluffy, about 3 minutes. Beat in egg yolks one at a time, then the melted chocolate and vanilla.

Reduce mixer to low. Add flour mixture in three additions, alternating with buttermilk in two additions, beginning and ending with flour. Mix just until combined.

In a clean bowl, beat egg whites to stiff peaks. Fold one-third into the batter to lighten, then fold in the rest until no white streaks remain. Divide between pans and bake 30-35 minutes, until a toothpick comes out clean. Cool in pans 10 minutes, then turn out onto racks to cool completely.

Combine evaporated milk, sugar, butter, and egg yolks in a medium saucepan over medium heat. Cook, stirring constantly, until thickened and golden brown, about 10-12 minutes. It should coat the back of a spoon and leave a trail when you drag your finger through it.

Remove from heat and stir in vanilla, coconut, and pecans. Cool to room temperature, stirring occasionally, until thick enough to spread. This takes about 1 hour.

Place one cake layer on a serving plate. Spread with half the frosting. Top with second layer and spread remaining frosting over the top, leaving sides bare. The frosting sets as it sits, so serve at room temperature.