For the cake

1. Prep oven and pan. Heat oven to 400 degrees F. Lightly butter a half-sheet pan (18 x 13 x 1 inch). Set aside.
2. Prep coffee and cocoa. In a small bowl, stir together instant coffee powder and hot water together until coffee is dissolved. In a small saucepan, stir butter, coffee mixture, cocoa powder and vegetable oil together over medium heat. Cook until mixture is smooth. Remove from heat. Set aside.
3. Mix dry ingredients. In a large bowl, whisk together flour, sugar, baking soda and salt until blended.
4. Add cocoa mixture. To the dry ingredients, whisk in cocoa mixture and mix until blended. Set aside.
5. Mix in wet ingredients. Whisk buttermilk, eggs and vanilla in medium bowl until blended. Add to flour mixture and stir until blended.
6. Bake. Spread batter in prepared pan.  Bake cake until tester inserted into center comes out clean, about 20 minutes. Transfer cake to rack to cool.

 For the icing

1. Prep cocoa mixture. As cake cools, stir milk, butter and cocoa in large saucepan over medium heat until smooth. Bring mixture to boil, stirring constantly. Remove from heat.
2. Add in. Add powdered sugar and vanilla and whisk until icing is relatively smooth. Let icing cool until it is warm and pourable but not hot.
3. Spread. Pour icing over warm cake and spread.  You want the icing and cake to be warm enough so that icing will spread and even out but not so hot that it immediately runs off the sides of the cake. Use an offset spatula to smooth out the icing where necessary.
4. Garnish. If you’re using chopped pecans, sprinkle the pecans on top while the icing is still warm so they will stick. If using chocolate curls, let cake cool almost completely before sprinkling chocolate curls on top.
5. Serve. Cool cake completely before cutting and serving.