Prepare the Oven and Pan: Preheat your oven to 400°F (200°C) and grease a sheet pan.
Mix Dry Ingredients: In a large bowl, mix together the flour, sugar, and cocoa powder.
Make the Chocolate Mixture: In a small saucepan, combine the water, butter, shortening, and German baking chocolate. Bring to a boil over medium heat, stirring until smooth and fully combined.
Combine Wet and Dry Ingredients: Add the chocolate mixture to the dry ingredients and whisk until well combined.
Add Remaining Ingredients: Stirring between each addition, first add the buttermilk, then the baking soda, salt, eggs, and vanilla.
Bake the Cake: Transfer the batter to the prepared sheet pan and bake for 20-22 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely before frosting.
For the Frosting:
Prepare the Frosting Base: In a medium-sized saucepan, combine the evaporated milk, egg yolks, butter, and both sugars. Bring the mixture to a boil over medium heat, then lower the heat to a simmer. Stir frequently and continue cooking for 10-12 minutes, or until the mixture has thickened.
Add Mix-Ins: Remove the frosting mixture from the heat and stir in the shredded coconut, chopped pecans, and vanilla extract.
Cool and Frost: Allow the frosting to cool slightly before spreading it over the cooled cake.
Chill and Serve: Chill the cake in the refrigerator for 1-2 hours before serving.
Enjoy your homemade German Chocolate Sheet Cake! It’s a perfect blend of rich chocolate and sweet, nutty frosting that’s sure to be a hit.
