Preheat oven to 350°F and prepare 3 cake pans with parchment and grease.
Melt German sweet chocolate in boiling water; set aside to cool.
Sift together flour, cocoa powder, baking soda, baking powder, and salt.
Cream butter and sugar until light and fluffy.
Beat in egg yolks one at a time, then add melted chocolate and vanilla.
Alternately add dry ingredients and buttermilk to the butter mixture, starting and ending with dry.
Whip egg whites to stiff peaks and fold gently into batter.
Divide batter evenly and bake for 25-30 minutes until a toothpick comes out clean.
For frosting, cook butter, sugars, evaporated milk, and egg yolks, stirring constantly until thickened.
Remove from heat, stir in vanilla, coconut, and pecans; cool before spreading.
Assemble cake by layering with coconut-pecan frosting and optionally chocolate buttercream on outside.