Ingredients:

  • 226g unsalted butter
  • 235ml water
  • 35g unsweetened cocoa powder
  • 250g all-purpose flour
  • 200g granulated sugar
  • 200g light brown sugar, packed
  • 1 tsp baking soda
  • 0.5 tsp salt
  • 2 large eggs, room temperature
  • 120ml buttermilk
  • 1 tbsp vanilla extract
  • 113g unsalted butter (for icing)
  • 90ml whole milk
  • 30g unsweetened cocoa powder (for icing)
  • 450g powdered sugar, sifted
  • 1 tsp vanilla extract (for icing)
  • 1 cup chopped pecans

Instructions:

  1. Preheat the oven to 350°F (175°C) and grease an 18x13-inch jelly roll pan. Note: Greasing well is crucial for easy serving later.
  2. Combine 226g butter, water, and 35g cocoa powder in a large saucepan over medium heat.
  3. Bring to a rolling boil for 30 seconds until the mixture is dark, glossy, and fragrant.
  4. Remove from the heat and whisk in the flour, granulated sugar, brown sugar, baking soda, and salt. Note: Whisk vigorously to remove any dry clumps.
  5. Whisk the buttermilk, eggs, and 1 tbsp vanilla in a small bowl until combined.
  6. Incorporate the egg mixture into the warm chocolate batter until the batter is smooth and slightly bubbly.
  7. Pour the batter into the pan and bake for 20 minutes until the center springs back when lightly touched.
  8. Boil 113g butter, milk, and 30g cocoa powder in a clean saucepan during the last 5 minutes of baking.
  9. Remove from heat and whisk in the sifted powdered sugar, vanilla, and pecans until the icing is thick and pourable.
  10. Pour the warm icing over the cake immediately until the entire surface is covered in a chocolate sheet.