German Chocolate Texas Sheet Cake with Coconut-Pecan Frosting

Step 1
Preheat the oven to 350 degrees F (175 degrees C). Spray an 11×17-inch sheet pan with cooking spray.

Step 2
Place chocolate and water in a large microwave-safe bowl. Microwave on high for 1 minute. Stir and continue cooking until chocolate is almost melted, about 30 seconds longer. Remove from microwave and stir until chocolate is completely melted.

Step 3
Beat egg whites in a glass, metal, or ceramic bowl until stiff peaks form.

Step 4
Combine sugar and butter in a large bowl; beat with an electric mixer until smooth and creamy. Add egg yolks to the sugar mixture, 1 at a time, beating well after each addition. Blend in melted chocolate and vanilla extract.

Step 5
Stir together flour, baking soda, and salt in a separate bowl. Add flour mixture to sugar-butter mixture alternating with buttermilk, beating batter until well blended after each addition. Add egg whites and stir gently until incorporated. Spread batter into the prepared pan.

Step 6
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 28 to 30 minutes. Cool on a wire rack, about 30 minutes.

Step 7
While cake is cooling, prepare the frosting. Combine evaporated milk, sugar, butter, egg yolks, and vanilla extract in a large saucepan over medium heat; bring to a boil. Reduce heat to low and cook, stirring occasionally, until thickened, 10 to 12 minutes. Remove from the heat and stir in coconut and pecans. Mix the frosting until cooled but still spreadable. Spread on top of cooled cake.