Ingredients:

  • 2 cups all-purpose flour (250g)
  • 2 cups granulated sugar (400g)
  • 0.5 tsp salt (3g)
  • 1 cup unsalted butter (227g)
  • 0.25 cup unsweetened cocoa powder (25g)
  • 1 cup boiling water (240ml)
  • 0.5 cup buttermilk (120ml)
  • 2 large eggs, room temperature
  • 1 tsp baking soda (6g)
  • 1 tsp vanilla extract (5ml)
  • 0.5 cup unsalted butter for glaze (113g)
  • 0.25 cup unsweetened cocoa powder for glaze (25g)
  • 6 tbsp whole milk (90ml)
  • 3 cups powdered sugar, sifted (375g)
  • 1 tsp vanilla extract for glaze (5ml)
  • 1 cup chopped pecans or walnuts (optional)

Instructions:

  1. Preheat your oven to 375°F (190°C). Thoroughly grease an 18x13 inch rimmed sheet pan with butter or non-stick spray. In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, and salt until well combined.
  2. In a medium saucepan, combine 1 cup of butter, 1/4 cup cocoa powder, and 1 cup of water. Bring the mixture to a rolling boil over medium heat while whisking constantly. Once boiling, remove from heat and immediately pour over the flour mixture. Stir until just combined.
  3. In a separate small container, whisk together the buttermilk, eggs, baking soda, and 1 tsp vanilla extract. Pour this mixture into the warm chocolate batter and whisk until the batter is smooth. Pour the batter into the prepared sheet pan.
  4. Bake for 18–22 minutes, or until a toothpick inserted into the center comes out with only a few moist crumbs. Do not overbake.
  5. While the cake is in its final 5 minutes of baking, prepare the glaze. In the same saucepan, boil 1/2 cup butter, 1/4 cup cocoa powder, and 6 tbsp milk. Remove from heat and whisk in the powdered sugar and the remaining vanilla until glossy. Stir in nuts if using.
  6. While the cake is still warm from the oven, pour the hot glaze over the top, spreading it evenly to the edges. Allow to set before slicing into 24 squares.