German Chocolate Cake

🧑‍🍳 INGREDIENTS : FOR THE CAKE 4 oz semisweet chocolate, chopped ½ cup water 4 eggs, whites and yolks separated 2¼ cups all-purpose flour, spooned into measuring cup and leveled off ¼ cup unsweetened natural cocoa powder, such as Hershey’s, sifted 1 teaspoon baking soda ½ teaspoon salt 2 sticks (1 cup) unsalted butter, softened 2 cups granulated sugar 1 teaspoon vanilla extract 1 cup buttermilk (see note) FOR THE COCONUT-PECAN FROSTING 4 egg yolks 1 (12-oz) can evaporated milk 1½ cups (packed) light brown sugar 1½ sticks (¾ cup) unsalted butter, cut into small pieces 2½ cups (lightly packed) sweetened flaked coconut (preferably Baker’s)