Makes 1 9-inch cake
FOR THE CAKE: 8 ½ tablespoons unsalted butter (1 stick plus 1/2 tablespoon), more for greasing pan ½ cup plus 1 1/2 tablespoons cake flour, more for flouring pan 1 cup bittersweet chocolate 6 large eggs, yolks and whites separated ¾ cup plus 1 tablespoon powdered sugar ¼ teaspoon kosher salt ⅓ cup plus 1 tablespoon granulated sugar ¼ cup plus 1 teaspoon cornstarch FOR THE FILLING: 1 cup apricot jam FOR THE GLAZE: 1 cup granulated sugar 1 ¼ cups bittersweet chocolate, chopped ½ cup water
NOTE: For camp we'll be making these as cupcakes! You will need a cupcake pan and liners.
1 Place a baking sheet in the oven and heat it to 350°F. Line bottom of a 9-inch cake pan with parchment paper. Butter and lightly flour sides of the pan.
2 Make the cake: Place chocolate and butter in a metal bowl set over a saucepan of simmering water and melt, stirring, until smooth. Set aside.
3 Place egg yolks in bowl of a stand mixer fitted with whisk attachment. Place whites in a separate, clean bowl.
4 Add powdered sugar to yolks and whip together until fluffy, creamy and pale, about 5 minutes. With the mixer on, slowly drizzle in the melted chocolate and butter, and beat until fluffy and incorporated.
5 Add salt to the bowl of egg whites and start beating them with a whisk or electric mixer. When whites show soft peaks, slowly add granulated sugar as you continue to beat. Do this until sugar has dissolved and egg whites are stiff and glossy.
6 In a separate bowl, sift together flour and cornstarch.
7 Fold a third of the flour mixture into egg yolk mixture. Fold a third of the egg whites into egg yolk mixture. Repeat two more times, alternating flour mixture and then egg whites, until no white streaks remain.
8 Gently scrape batter into prepared pan and smooth top. Place on baking sheet in oven and wedge the handle of a wooden spoon in the oven door. Bake for 10 minutes and then remove spoon. Lower heat to 275 °F, and bake for 40 to 45 minutes longer, or until a tester inserted into the cake's center comes out clean.
9 Place cake pan on a rack for 10 minutes to cool, then invert cake, remove pan and peel off parchment paper. Let cake cool completely upside down. Once cooled, set a cardboard cake circle on the cake and flip back over. Slice it in half horizontally into two layers. Place rack over a piece of parchment paper and move top half of cake to a large plate.
10 Make the filling: Place jam and 2 Tablespoons water in a small pan, bring to a boil and continue to boil for a minute or two. Push apricot mixture through a sieve to get a smooth consistency. Let cool, then spread half of the mixture evenly on the bottom cake layer. Place second layer on top of the jam and press down slightly. Spread remaining jam over top and sides of cake. Let cool completely.
11 Make the glaze: Place the sugar, water, and chocolate in a small saucepan and bring to a boil, stirring frequently. Clip a candy thermometer to the side of the pan. Boil, stirring frequently, until the glaze reaches 230°F, about 5 minutes. The mixture will be smooth, glossy, and pourable and will coat the back of a spoon. Remove from the heat and let stand just until the bubbles die down.
12 Slowly pour warm chocolate glaze evenly all over cake, letting excess drip down sides. Avoid using a spatula to spread glaze: It will stay glossiest if not touched. Reserve a little glaze in the pan to pour over any uncoated patches on the sides so that entire cake is coated. Gently wedge two spatulas under cake, using cardboard round to transfer it to a serving plate. Let glaze set completely before cutting and serving.