You’ll need:

For the Cake:

  • Nonstick vegetable oil spray
  • 1 1/4 cups all-purpose flour
  • 1 cup sugar
  • 3/4 cup natural unsweetened cocoa powder
  • 1 1/2 teaspoons kosher salt
  • 1 teaspoon baking soda
  • 1/4 cup vegetable oil
  • 1 teaspoon vanilla extract
  • 1/2 cup finely chopped semisweet or bittersweet chocolate (3 1/2 ounces)

For the Peanut Butter Buttercream:

  • 1/2 cup sugar
  • 1/4 cup egg whites (from about 2 large eggs)
  • 1 1/2 teaspoons vanilla extract
  • 1/4 cup creamy peanut butter
  • 6 tablespoons (3/4 stick) chilled unsalted butter, cut into 1/4-inch cubes
  • Kosher salt
  • 1/4 cup chopped semisweet or bittersweet chocolatet(about 1 3/4 ounces)
  • 1/4 cup chopped unsalted, dry-roasted peanuts

PREPARATION

Chocolate Cake

  • Preheat oven to 350°. Coat bottom and sides of pan with nonstick spray; line bottom of pan with parchment paper. IMG_6207Whisk flour and next 4 ingredients in a large bowl. IMG_6208Add oil, vanilla, and 1 1/4 cups water; whisk until smooth. IMG_6209 IMG_6210 Fold in chopped chocolate. IMG_6213Scrape into prepared pan; smooth top. IMG_6214Bake until a tester comes out clean when inserted into center, 35–40 minutes. Let cool completely in pan on a wire rack.

Peanut Butter Buttercream

  • Combine sugar and egg whites in a medium metal bowl set over a saucepan of simmering water. IMG_6215Whisk constantly until sugar dissolves and mixture is hot to the touch, 3–4 minutes. IMG_6216Remove from heat; using an electric mixer, beat on high speed until cool and thick, 5–6 minutes. IMG_6217IMG_6218Beat in vanilla, then peanut butter. With mixer running, add butter a few pieces at a time, beating to blend between additions.IMG_6220IMG_6221IMG_6222 Season with salt.
  • Run a thin knife around pan to release cake. Invert cake onto a serving plate. Spread peanut butter buttercream over top. Garnish with chopped chocolate and peanuts. DO AHEAD: Can be made 1 day ahead. Store airtight at room temperature.IMG_6235
  • Cut into 2-inch squares.IMG_6242