Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans, then line them with parchment paper.

Lower the temperature to 325°F (160°C). In a mixing bowl, beat cream cheese and sugar until silky smooth. Add one egg and vanilla, mixing until well combined. Pour into a prepared 9-inch round pan and bake for 25–30 minutes, or until set. Cool and refrigerate.

In a saucepan, melt 1 ½ cups of German chocolate and ¾ cup butter over low heat, stirring frequently. Let it cool slightly.

In a separate bowl, beat granulated sugar, brown sugar, and egg yolks together until fluffy. Stir in the cooled chocolate and vanilla.

In another bowl, whisk together the flour, baking powder, baking soda, and salt. Alternately add this dry mixture and buttermilk to the wet ingredients in three batches, mixing gently until combined.

In a clean bowl, beat egg whites until stiff peaks form, then fold into the chocolate batter.

Divide the batter evenly into the three prepared pans. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean. Cool for 10 minutes in the pans before transferring to wire racks to cool completely.

Melt remaining German chocolate and butter in a saucepan over low heat. Let it cool slightly.

In a medium bowl, beat together powdered sugar, milk, and vanilla until smooth. Add your cooled chocolate mixture to create the frosting.

To assemble, place the first cake layer on a serving platter and generously spread frosting on top. Gently place the chilled cheesecake layer on top, then add the second cake layer with more frosting. Place the final cake layer on top and frost both the top and sides. Sprinkle with chopped walnuts or pecans.