Softened butter, for greasing pans
1/2 cup natural unsweetened cocoa powder
2 ounces 100% cacao dark chocolate (such as Lindt, Perugina, or Valrhona), finely chopped
1 cup cream stout
1 1/3 cup cake flour
1/2 teaspoon baking soda
1/4 teaspoon salt
1 cup (packed) dark brown sugar
1/2 cup canola oil
2 large eggs
1 teaspoon vanilla extract
1 cup granulated sugar
1/4 cup butter
1 cup peanuts
1 teaspoon kosher salt
1/4 cup unsalted butter
1 cup brown sugar
1/2 teaspoon cinnamon
2 bosc pears, cored and cut into 1 inch pieces (about 2 1/2 cups)
1 cup butter, softened
3/4 cup confectioner’s sugar
6 ounces 100% cacao dark chocolate (such as Lindt, Perugina, or Valrhona), finely chopped
6 ounces 70% cacao dark chocolate (such as Lindt, Perugina, or Valrhona), finely chopped
1/4 cup cocoa powder
1/4 cup cream stout, hot
2 cups butter, softened
1 1/4 cup confectioner’s sugar
The cake can be 1 day ahead. Store refrigerated and bring to room temperature before serving. The pear caramel and chocolate frostings can be made 2 days ahead; store covered in the refrigerator. Bring to room temperature and re-mix in a stand mixer before spreading. The peanut toffee can be made up to 3 days ahead. Store covered in an airtight refrigerator at room temperature
Position a rack in the center of the oven; and preheat to 350°F. Butter two 9-inch cake pans with 2-inch-high sides. Line the bottom of pans with parchment paper and butter the parchment. In a medium bowl, combine the cocoa powder and dark chocolate. In a small saucepan, bring the cream stout to a boil. Pour the boiling cream stout over the chocolate and whisk until the mixture is smooth.
In a separate medium bowl, whisk to combine the flour, baking soda, and salt. Using an electric mixer fitted with the whisk attachment, mix the brown sugar, oil, eggs, and vanilla over medium-high speed for about 1 minute, or until well blended. Add the flour and chocolate mixtures and mix over medium speed until blended (the batter will be thin). Divide the batter between the prepared pans.
Bake the cakes for about 16 minutes, or until a tester inserted into the center comes out with some crumbs attached. Cool in pans on baking racks for 15 minutes. Turn the cakes out onto racks and peel off the parchment. Turn the cakes over and leave to cool.
Line a baking sheet with a silpat or lightly oiled parchment paper.
In a small heavy saucepan fitted with a candy thermometer, combine the sugar and 1/4 cup of water. Cover and bring the mixture to a boil over medium-high heat. After about 3 minutes, when the mixture is boiling and the sugar has dissolved, remove the lid and add the butter. Cook 1 minute longer and add the peanuts. Cook for about 5 minutes, or until the mixture has reached 300°F and has a deep caramel color. Remove from the heat, stir in the salt, and pour the mixture in an even layer onto the prepared baking sheet.
When the mixture has cooled completely, break it into 1/4-inch shards by hand.
In a large heavy skillet, melt the butter over low heat. Stir in the brown sugar and cinnamon. Cook over medium-low heat, stirring, until the sugar dissolves. Add the pears and cook in the caramel over medium heat for about 10 minutes, or until the pears are completely soft and caramelized. Transfer the mixture to a blender and puree until completely smooth. Set the pear caramel aside.
In the bowl of a stand mixer fitted with the paddle attachment, combine the butter, confectioner’s sugar, and 2/3 cup of the pear caramel and beat over medium speed for about 5 minutes, or until the mixture is light and fluffy. Set the pear caramel frosting aside and reserve the remaining pear caramel.
In a medium heatproof bowl set over barely simmering water, add the dark chocolates. Heat, stirring occasionally, until the chocolate has completely melted. Remove the bowl from the heat. Set aside to cool slightly.
In the bowl of a stand mixer fitted with the paddle attachment, mix the butter and confectioner’s sugar over medium speed for about 5 minutes, or until the mixture is light and fluffy. Lower the speed to medium-low and slowly drizzle in the cooled melted chocolate and mix until smooth.
In a small bowl, whisk to combine the cocoa powder and hot cream stout until the mixture is completely smooth. Add the cocoa-stout mixture to the mixer and mix over medium speed until incorporated. Set the dark chocolate frosting aside at room temperature.
Using a serrated knife, trim the cooled cakes to an even thickness. Cut a piece of cardboard that is just smaller than the diameter of the cakes. Place the cardboard on a cake spinner. Place a small dollop of the dark chocolate in the middle of cardboard piece to anchor the cake. Place 1 cake bottom-side-down on the cardboard. Lay the pear caramel frosting on the top of the cake and, using a large palette knife, spread the frosting in an even layer to cover the top of the cake. Using the palette knife and cake spinner, smooth the frosting over and scrape off any overhanging frosting.
Place the other cake bottom-side-up on top of the pear caramel frosting, making sure the edges of each cake are lined up. Lightly press down on the top cake to flatten. Place about 1/2 cup of the dark chocolate frosting on the top of the cake and, using a palette knife, spread the frosting over the cake in a thin layer. Using the overhanging frosting and extra frosting as needed, spread a thin layer over the sides of the cake. Set the cake in the refrigerator for about 15 minutes to harden the frosting.
Remove the cake from the refrigerator and place about 1 cup of frosting on top of the cake. Spread the frosting in an even layer over the cake. Use the overhanging frosting and extra frosting as needed to spread an even layer of frosting over the sides of the cake. Press the peanut toffee shards into the side of the cake and transfer to the refrigerator to chill.
Remove the cake from the refrigerator and leave at room temperature for 10 minutes. Cut the cake into slices, serving the remaining pear caramel and peanut toffee shards alongside.