Jack-and-Coke Sheet Cake

Preparation

1. For the Cake:  Preheat oven to 350ºF. Spray an 18-by-12-inch sheet cake pan with baking spray.
2. Pour the Coke into a large saucepan and add the butter, the cocoa powder, and the whiskey. Cook over medium heat, stirring frequently, until the butter is melted and the mixture is smooth. Whisk the flour, sugars, baking soda, and salt together in a large bowl until well combined. When the butter is melted, remove the pot from the heat and stir the cocoa mixture into the dry ingredients until completely blended and smooth. Measure the buttermilk into a 2-cup jug or liquid measuring cup, then break in the eggs and add the vanilla. Beat the eggs with the buttermilk and vanilla, then add this to the batter and stir until it’s completely combined. Stir in pecans (if using). Spread the batter into the prepared pan in an even layer, all the way to the corners. Bake for 15 to 20 minutes, until a tester inserted in the center comes out clean. Make the frosting while the cake is in the oven.
3. For the Frosting:  Wipe out the saucepan and melt the butter with the Coke, whiskey, and cocoa powder over medium heat, stirring until combined. Beat in the confectioners’ sugar about a cup at a time until the frosting is smooth and combined. Take the cake from the oven and pour the frosting over it, covering as much cake as possible. Tilt the cake pan or use a spatula to cover the entire surface, working quickly before the frosting begins to set. Leave the cake to cool. The cake can be made up to 2 days ahead and kept covered in a cool place.