Triple Decker Peanut Butter Brownies

For the Brownie Layer - Adjust oven rack to middle position and preheat oven to 350°F (180°C). Line an 8-by-8-inch baking pan with two 8-inch-wide strips of parchment paper so that all sides are covered with a 1-inch overhang. Lightly grease parchment with butter; set aside.

For the Brownie Layer - In a large microwave-safe bowl, combine chocolate and butter. Microwave on high, stirring every 30 seconds, until melted and smooth, about 2 minutes. (Alternatively, nest bowl over a saucepan of simmering water and melt chocolate and butter, stirring occasionally, until melted and smooth, about 5 minutes.) Whisk sugar, brown sugar, and salt to incorporate. Add peanut butter, eggs, egg yolk, and vanilla until smooth.

For the Brownie Layer - Using a fine-mesh sieve, sift flour and cocoa powder into chocolate mixture, and whisk until just combined. Pour into prepared baking pan and, using an offset or flexible spatula, smooth top. Bake until just set and a toothpick inserted into center comes out with moist crumbs, 20 to 30 minutes. Transfer to wire rack and let cool completely.

For the Peanut Butter Layer - In a stand mixer fitted with the paddle attachment or in a large bowl and using an electric hand mixer, beat peanut and butter on medium speed until creamy, 1 to 2 minutes. Add confectioners' sugar, vanilla, and salt, and beat until fully incorporated and mixture is smooth and creamy. Scrape over cooled brownies and, using an offset spatula, spread peanut butter from edge to edge to evenly cover. Refrigerate while you prepare ganache topping.

For the Ganache Topping - In a medium bowl, combine chocolate, confectioners' sugar, and peanut butter. In a small saucepan, bring cream to a simmer over medium-high heat, about 2 minutes. Pour cream over chocolate and whisk until smooth. Pour over peanut butter layer and refrigerate until firm, 2 to 3 hours.

Final Step - Hold and lift parchment paper to remove brownies from baking pan. Gently transfer to a cutting board. Using a hot knife, slice brownie into 16 squares. (For cleaner cuts, run knife under warm water and dry knife with a clean kitchen towel before portioning each slice.)