6tablespoonsunsalted butter cut into 1/4-inch cubes,chilled
pinch of salt
1/4cupfinely chopped semi-sweet chocolate
1/4cupchopped dry-roasted peanuts
Preheat oven to 350 degrees. Coat an 8-inch square pan with cooking spray. Line bottom with parchment paper.
In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda.
Add oil, vanilla extract and 1 1/4 cups water and stir until smooth. Fold in 1/2 cup chopped chocolate.
Pour into prepared pan and bake for 35-40 minutes. Cool completely in pan.
To make frosting, combine sugar and egg whites in a medium metal bowl set over a saucepan of simmering water. Continuously whisk until sugar dissolves and mixture is hot to the touch, about 3 to 4 minutes.
Transfer mixture to the bowl of an electric stand mixer and beat with whisk attachment until cool and thick, about 5-6 minutes.
Beat in vanilla extract and then peanut butter.
With mixer on medium-high, add butter pieces a few at a time. Beat until butter is completely incorporated. Add a pinch of salt.
Run a knife around edges of cake and turn it out onto a plate or cake stand. Peel parchment paper off and top with frosting, chopped chocolate, and peanuts.