Chocolate Rolled Cake with Brown Sugar Buttercream and Chopped Pistachios
2 cups (280 g) all purpose flour
1 teaspoon baking powder
1/2 teaspoon baking soda
1/4 teaspoon sea salt
3 oz (85 g) bittersweet chocolate (preferably something over 65% cacao), chopped into 1/4 inch chunks
3/4 cup (170 g or 1 1/2 sticks) unsalted butter at room temperature
1 cup (200 g) white granulated sugar, divided
3/4 cup (165 g) dark brown sugar
4 large eggs, separated
2 teaspoons vanilla extract
1 teaspoon almond extract (optional)
1 cup buttermilk, well shaken
Brown Sugar Buttercream
3 large egg whites
3/4 cup (165 g) dark brown sugar
1/2 teaspoon sea salt
1 cup + 2 tablespoons (255 g or 2 1/4 sticks) unsalted butter, cool but not cold
3/4 cup (105 g) chopped unsalted pistachio nuts (if you can only find salted nuts, omit the salt in the buttercream)
1. Preheat the oven to 350˚F and spray a 12 x 17 rimmed baking sheet with cooking spray. Line the bottom with a piece of parchment paper and spray the parchment paper with cooking spray too.
2. Place the flour, baking powder, baking soda, and salt in a large mixing bowl. Using a balloon whisk, vigorously stir the dry ingredients until they are well blended together. Place the chocolate in a microwave safe bowl and microwave for 30 seconds on high. Stir and microwave again for 30 seconds. Stir until the chocolate is melted, heating the chocolate in additional 15 second intervals in the microwave if necessary.
3. Place the butter and 3/4 of the white sugar (reserving the other 1/4 for later) and all of the brown sugar in the bowl of standing mixer and cream until the butter is light and creamy (about 2 to 4 minutes, depending on the temperature of the butter). You may want to scrape down the side of the bowl in the middle. Scoop up two or three tablespoons of the whipped butter and fold it into the melted chocolate until incorporated. Scrape the chocolate into the butter and beat the mixture on low speed until the chocolate is incorporated. Add two egg yolks and beat to incorporate. Scrape down the sides and add the second two egg yolks and beat to incorporate. Add the vanilla and almond extract and beat to incorporate.
4. Add 1/2 cup of the buttermilk to the batter and beat to incorporate. Add 1/2 of the dry ingredients and beat to incorporate. Repeat with the remaining buttermilk and remaining dry ingredients, scraping down the sides of the bowl in between additions. In a clean bowl, whip the egg whites on medium high speed until they form soft peaks. Slowly pour the reserved 1/4 cup white sugar into the whipped egg whites until the whites become glossy and hold stiff peaks. Add half of the egg whites to the cake batter and fold gently to incorporate. Add the rest of the egg whites, folding to incorporate.
5. Scrape the batter into the prepared baking sheet and spread evenly over the pan. Bake the cake for 22 to 27 minutes or until a toothpick inserted in the middle comes out clean and the cake feels firm to the touch. Let cool completely in the pan before assembly the cake.
6. Once the cake has cooled, make the buttercream frosting by placing the egg whites, brown sugar and salt in the metal bowl of a standing mixer. Place the bowl over a pot of simmering water and whisk by hand the egg whites until the sugar and salt have dissolved and the temperature reaches 160˚F (warm to the touch). Pull the bowl off the water and place in the stand mixer fitted with a wire whisk attachment. Beat the egg whites on high speed until stiff peaks form. Reduce the speed to medium and beat for an additional 5 to 6 minutes until the egg whites have cooled and are fluffy. Switch out the whisk attachment for the paddle attachment and turn the speed to medium low. Add 2 tablespoon of the butter at a time, waiting for the butter to incorporate before adding more butter. Continue to beat all the butter into the frosting. Once the butter has all been added, reduce the speed to low and beat for an additional 2 to 3 minutes to smooth the buttercream and get rid of any air bubbles. If the buttercream looks like it is broken, turn the speed to medium high and beat for a minute or two to bring it back together.
7. Assemble the cake by first placing the cake with the long side facing you. First trim 1/2 inch off the edges on the left and right to make a proper rectangle. Cut the cake in half with a serrated knife, making two 12 x 8 inch rectangles. Further split each rectangle in half again, to make four 12 x 4 inch rectangles. Lift the cake up and cut the parchment paper underneath the cake, right where you cut the cake, so the parchment paper is also split with the cakes. Spread about half the buttercream over the cake and then sprinkle 1/2 cup of the chopped pistachios over the frosting evenly.
8. Roll the first strip of cake by tucking the cake into the roll and continuing to roll tightly, peeling the parchment paper as you tuck and roll. Place the rolled cake upright in the middle of the serving platter so you can see the roll on top. Then take the second strip of cake and wrap it around the first rolled piece of cake. Continue with the third and fourth piece, wrapping the cake around each other in a spiral pattern. You might have to trim some of the cake off to make it fit properly in the end, but don’t worry too much about it. Once you’ve rolled all the cake, frost the outside of the cake with the remaining frosting, making sure to leave the top of the cake exposed for everyone to see. If you want to get fancy you can use a cake comb around the outside of the cake but don’t feel like that’s necessary. Sprinkle some of the remaining chopped pistachios on top of the cake, where the frosting is, to help cover up some of the big holes and gaps in the cake roll, and then gently press the remaining chopped pistachios at the bottom of the cake about an inch up. Serve immediately or keep it in the fridge for up to three or four days, bringing to room temperature before serving.