Start to finish: 1 hour 40 minutes, plus cooling and chilling
Bête noire is a flourless chocolate cake that gets its silky, ultra-smooth, almost custard-like texture from the sugar syrup in the base, as well as from gentle baking. We bring a uniquely complex flavor to our version by caramelizing sugar with black peppercorns before dissolving the caramel with orange juice and bourbon. A combination of bittersweet and semi-sweet chocolate yields a rounder, richer finish than just one type of chocolate, while Angostura bitters lend a spiciness and depth that balance the sweetness of the dessert. We forgo the classic ganache coating and opt to use quickly candied orange zest for a garnish that adds contrasting color and texture. Though the cake requires at least 4 hours of chilling to fully set, it’s best served at room temperature, so be sure to remove the cake from the refrigerator at least two hours before serving. For neat slices, dip the knife in hot water, then wipe it dry before each cut.
Don’t use a whisk to combine the ingredients for the batter; a large silicone spatula is better. A whisk incorporates air, which leads to bubbles rising to the surface during baking and marring the smooth, shiny surface. Also, don’t forget to run a knife around the edges of the cake the moment it comes out of the oven; loosening the edges from the sides of the pan prevents the cake from cracking as it cools. Finally, don’t cover the cake before refrigerating, as a cover may trap condensation that can drip onto the cake.
Heat the oven to 275°F with a rack in the middle position. Coat the bottom and sides of a 9-inch springform pan with butter. Line the bottom of the pan with kitchen parchment, then butter the parchment. Set a wire rack in a rimmed baking sheet. In a large bowl, combine the bittersweet and semi-sweet chocolates and the butter; set a fine mesh strainer across the bowl, then set aside.
Using a vegetable peeler, remove just the outer zest of the orange, not the white pith beneath, in long strips; set the strips aside. Halve the orange and juice it into a liquid measuring cup. Measure 3 tablespoons of the juice into a medium saucepan. Add the bourbon to the remaining juice in the measuring cup, then add enough water to equal 1 cup total liquid; set aside.
Add the 160 grams (¾ cup) sugar to the juice in the saucepan, then add the zest strips and peppercorns. Set over medium-high and cook, without stirring but occasionally swirling the pan, until the sugar dissolves, 1 to 2 minutes. Continue cooking, swirling the pan often, until the sugar caramelizes to deep mahogany brown and the peppercorns begin to pop, 4 to 5 minutes. Remove the pan from the heat and carefully pour in the orange juice–bourbon mixture; the caramel will bubble up and harden. Set the pan over medium, bring to a simmer and cook, stirring, until the caramel has dissolved, and the peppercorns no longer stick together, 1 to 2 minutes. Remove from the heat and stir in the bitters.
Immediately pour the hot sugar syrup through the strainer into the chocolate-butter mixture; reserve the strained solids. Jostle the bowl to ensure the chocolate and butter are fully covered with syrup, then let stand for 2 to 3 minutes. Using a silicone spatula, gently stir until the mixture is well combined and completely smooth; it should be barely warm.
Add the beaten eggs to the chocolate mixture and stir with the spatula until homogeneous and glossy, 2 to 3 minutes. Pour into the prepared springform pan. Gently tap the sides of the pan to remove any air bubbles, then use the back of a spoon to smooth the surface. Set the pan on the prepared baking sheet and bake until the cake barely jiggles when the pan is gently shaken, about 45 minutes.
Remove from the oven and immediately run a thin, sharp knife around the edges to loosen the sides of the cake from the pan. Cool to room temperature in the pan, then refrigerate uncovered for at least 4 hours or up to 24 hours.
While the cake cools, transfer the zest strips from the strainer to a small, shallow bowl, removing and discarding any peppercorns stuck to them. Sprinkle the strips with the 70 grams (⅓ cup) sugar, then toss until the strips are completely coated. Cover loosely and store at room temperature until ready to serve.
About 2 hours before serving, remove the cake from the refrigerator. Remove the zest strips from the sugar and shake off excess sugar; reserve the sugar for another use. Cut the strips lengthwise* (see note with decoration instructions) into thin strips. Remove the sides of the springform pan. Arrange the zest slivers on the cake around the edges. Slice the cake and serve with small spoonfuls of yogurt.
FOR HEART DECORATION:
Unmold cooled cake and place on a sheet of parchment paper or aluminum foil.
Transfer chocolate to a baggie and push into a corner. Twist top of baggie securely. With scissors, snip off a very small portion of the baggie tip holding the chocolate.
Hold the baggie a few inches above the cake and beginning from one edge of the cake, squeeze the baggie gently while moving in long, fast sweeping motions over the cake, until you reach the opposite edge.
Break toothpicks in half and insert 3 halves in places to support the heart. Place heart cutout over toothpicks.
Place cocoa in a sieve and thoroughly dust the edges of the cake around the heart.
Remove the heart cutout and toothpicks.
*When slicing the strips of sugared orange peel, slice them crosswise (instead of lengthwise). Place the strips on the cake, framing the heart.