Better-Than-Mom's German Chocolate Cake

Preheat oven to 350°F (175°C). Grease and flour two 9-inch cake pans, lining the bottoms with parchment paper circles. (5 minutes)

In a double boiler, melt semisweet and unsweetened chocolates with water over simmering water, stirring until smooth. Set aside to cool slightly. (10 minutes)

In a large bowl, cream 1 1/4 cups sugar and butter until light and fluffy. Beat in the cooled chocolate mixture, then add egg yolks one at a time, mixing well after each addition. (8 minutes)

In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the creamed mixture, alternating with buttermilk, beginning and ending with dry ingredients. Stir in vanilla extract. (7 minutes)

In another bowl, beat egg whites until soft peaks form. Gradually add 1/4 cup sugar and beat until stiff, glossy peaks form. Gently fold the egg whites into the batter in two additions, being careful not to overmix. (10 minutes)

Divide batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. (35 minutes)

Let cool in pans for 10 minutes, then invert onto wire racks to cool completely. (10 minutes)

For the filling, whisk together heavy cream, sugar, and egg yolks in a saucepan. Cook over medium heat, stirring constantly, until the mixture thickens and coats the back of a spoon (about 8-10 minutes). Remove from heat and stir in coconut, pecans, butter, and salt until butter is melted and mixture is well combined. Let cool completely. (20 minutes)

For the syrup, combine water and sugar in a saucepan. Bring to a simmer, stirring until sugar is dissolved. Remove from heat and stir in rum. (5 minutes)

For the ganache, place chopped chocolate, butter, and corn syrup in a heatproof bowl. Heat cream in a saucepan until simmering. Pour hot cream over the chocolate mixture and let sit for 1 minute, then stir until smooth and glossy. Let cool slightly until spreadable. (15 minutes)

Using a serrated knife, level the tops of the cooled cake layers. Place one layer on a serving plate or cake stand. Brush with syrup. Spread with half of the coconut-pecan filling. Repeat with the remaining layers, syrup, and filling. (15 minutes)

Frost the top and sides of the cake with the chocolate ganache. Decorate as desired. Chill for at least 30 minutes before serving to allow the ganache to set. (10 minutes)