Ingredients

  • Cake
  • 2 cups all-purpose flour
  • 3/4 cup unsweetened cocoa powder, plus additional for dusting (not Dutch-process)
  • 1 1/4 teaspoons baking soda
  • 3/4 teaspoon salt
  • 1 cup unsalted butter, softened
  • 1 1/2 cups packed dark brown sugar
  • 2 large eggs
  • 1 teaspoon pure vanilla extract
  • 1 1/3 cups water
  • Frosting
  • 2 large egg whites
  • 1/2 cup sugar
  • 1/4 cup light corn syrup
  • 2 tablespoons water
  • 1 teaspoon pure vanilla extract

Method

  • To make cake:.
  • Preheat oven to 350°F with rack in middle. Butter and flour a 9-inch square cake pan (2 inches deep).
  • Whisk together flour, cocoa powder, baking soda, and salt.
  • Beat together butter and brown sugar with an electric mixer until pale and fluffy. Add eggs 1 at a time, beating well, then beat in vanilla.
  • Add flour mixture and water alternately in batches, beginning and ending with flour mixture and mixing until just combined.
  • Pour batter into cake pan and smooth top, then bake until a wooden pick inserted in center comes out clean, 45 to 55 minutes.
  • Cool in pan on a rack 1 hour.
  • Transfer cake to a cake plate.
  • Make frosting:.
  • Combine frosting ingredients with a pinch of salt in a metal bowl set over a saucepan of simmering water and beat with a handheld electric mixer at high speed until frosting is thick and fluffy, 6 to 7 minutes.
  • Remove bowl from heat and continue to beat until slightly cooled.
  • Mound frosting on top of cake.
  • Dust with additional cocoa powder.
  • Cooks' notes:.
  • Cake, without frosting, will improve in flavor if made 1 day ahead. Cool, then keep, wrapped in plastic wrap, at room temperature. Frost cake just before serving.
  • The egg whites in the frosting are not fully cooked. You can substitute pasteurized or reconstituted dried egg whites if salmonella is a problem in your area.