Chocolate Peanut Butter Cake
(Epicurious)

YIELDMakes 16 servings

INGREDIENTS

Chocolate 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)


Peanut butter buttercream:
  * 1/2 cup sugar
  * 1/4 cup egg whites (from about 2 large eggs)
  * 1 1/2 teaspoon vanilla extract
  * 1/4 cup creamy peanut butter
  * 6 tablespoons (3/4 stick) chilled unsalted butter, cut into 1/4" cubes
  * Kosher salt
  * 1/4 cup chopped semisweet or bittersweet chocolate (about 1 3/4 ounces)
  * 1/4 cup chopped unsalted, dry roasted pinenuts or peanuts
  * 
Special Equipment
An 8x8x2" cake pan

PREPARATION

For chocolate cake:
  - Preheat oven to 350°F. Coat bottom and sides of pan with nonstick spray; line bottom of pan with parchment paper. 
  - Whisk flour and next 4 ingredients in a large bowl. Add oil, vanilla, and 1 1/4 cups water; whisk until smooth. Fold in chopped chocolate. 
  - Scrape into prepared pan; smooth top. Bake until a tester comes out clean when inserted into center, 35-40 minutes. Let cool completely in pan on a wire rack.


For peanut butter buttercream:
  - Combine sugar and egg whites in a medium metal bowl set over a saucepan of simmering water. Whisk constantly until sugar dissolves and mixture is hot to the touch, 3-4 minutes. 
  - Remove from heat; using an electric mixer, beat on high speed until cool and thick, 5-6 minutes.
  -  Beat in vanilla, then peanut butter. With mixer running, add butter a few pieces at a time, beating to blend between additions. 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.
  - Cut into 2" squares.