Prepare and Bake the Cake: Preheat your oven to 350°F. Grease and flour a sheet pan. Optional: Line with parchment paper to be able to take the cake out of the pan.
Mix Dry Ingredients: In a large bowl, sift together 2 cups flour, 1½ cups sugar, ½ cup unsweetened cocoa powder, 1½ teaspoons baking soda, 1 teaspoon baking powder, and ¼ teaspoon salt.
Combine Wet Ingredients: In another bowl, whisk 2 room-temperature eggs, 1 cup vegetable oil (or melted butter), 1 cup room-temperature buttermilk, and 1 cup hot water (very warm, not boiling).
Combine Batter: Gradually mix the wet ingredients into the dry ingredients until smooth. Pour the batter into the prepared pan and spread evenly.
Bake: Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Poke and Add Sweetened Condensed Milk: Remove the cake from the oven and, while still warm, use the handle on a wooden spoon to poke holes all over the cake. Open a 14-ounce can of sweetened condensed milk and slowly pour it evenly over the cake, letting it seep into the holes.
Prepare the Chocolate Ganache Topping: Chop a 4-ounce bar of German Chocolate and heavy cream into a small saucepan. Heat until just melted then pour over the chocolate cake. Spread evenly pushing the chocolate into the poked holes.
Make the Pecan Coconut Topping: Combine Ingredients: In a saucepan, combine 1 cup evaporated milk, 1 cup sugar, and 3 lightly beaten egg yolks. Add ½ cup unsalted butter and 1 teaspoon vanilla extract. Heat the mixture over medium-low heat, stirring constantly until it thickens slightly (about 5-7 minutes). Remove from heat. Stir in 1⅓ cups sweetened shredded coconut and 1 cup chopped pecans. Spread the warm pecan coconut mixture evenly over the ganache layer on the cake.
Finish and Serve: Allow the entire cake to cool to room temperature so all layers set. Once cooled, slice the cake into squares and serve this decadent treat!
Enjoy your Irresistible German Chocolate Sheet Cake—a perfect blend of rich chocolate, creamy ganache, and a crunchy, sweet pecan coconut topping!