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)
An 8x8x2-inch cake pan or circular springform release metal pan
Preheat oven to 350°. 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.
Peanut Butter Icing
Use the $300 Icing as a base, cut butter in half from original recipe and whip in 1/2-3/4 cup peanut butter to taste.
Run a thin knife around pan to release cake. Invert cake onto a serving plate. Spread peanut butter icing over top. Garnish with chopped chocolate and peanuts. DO AHEAD: Can be made 1 day ahead. Store airtight at room temperature.