Heaven and Hell Sheet Cake

Name: Heaven and Hell Sheet Cake
Prep time: 37 min
Cook time: 35 min
Total time: 1 h 12 min
Cuisine: American
Ingredients: 2 cups all-purpose flour; 1 teaspoon baking soda; 1/4 teaspoon fine salt; 1 1/2 cups hot coffee; 3/4 cup unsweetened cocoa powder; 4 oz dark chocolate, finely chopped; 1/2 cup buttermilk, room temperature; 1 cup vegetable oil; 1/2 cup unsalted butter, room temperature; 2 cups packed light brown sugar; 2 large eggs, room temperature; 3/4 cup plus 2 tablespoons sugar; 1 tablespoon corn syrup; 4 egg whites; 1 1/4 teaspoons vanilla extract