Devil’s Inferno Cake

1. Cake: Preheat oven to 325°F. Butter two 9-inch round cake pans. Line bottoms with parchment rounds; butter parchment. Combine boiling water, cocoa, and chocolate in a bowl; stir until chocolate has melted. Let cool 10 minutes. Meanwhile, in another bowl, whisk together flour, baking powder, baking soda, and salt.

2. Beat butter with brown sugar on medium-high speed until light and creamy, 2 to 3 minutes. Beat in eggs, one at a time, blending well after each addition. Beat in vanilla, then chocolate mixture to combine. Reduce speed to low; beat in flour mixture in two additions, alternating with sour cream, until just combined.

3. Divide batter evenly between prepared pans, smoothing tops with an offset spatula. Bake until a tester inserted into centers comes out clean, 35 to 40 minutes. Let cakes cool in pans on a wire rack 20 minutes. Turn out cakes and place on rack, top-sides up; let cool completely. With a serrated knife, trim tops of cakes so they are level.

4. Buttercream: In the bowl of a mixer, whisk together granulated sugar and egg whites. Place over (but not in) a pot of simmering water; continue whisking constantly until sugar has completely dissolved and mixture is warm, 2 to 3 minutes. Place bowl in mixer fitted with the whisk attachment and beat on high speed until thick, glossy, and cool, 8 to 10 minutes.

5. Switch to paddle attachment. Beat in butter, 2 tablespoons at a time, on medium-high speed until combined. Beat in chocolate. Reduce speed to low and continue beating until air bubbles are gone, 1 to 2 minutes more.

6. Flames: Line several baking sheets with parchment. In a small saucepan, combine granulated sugar and 1/4 cup water over medium-high heat, stirring until sugar has dissolved. Bring to a boil and cook, swirling pan occasionally, until mixture registers 300° to 310° (hard-crack stage) on a candy thermometer, 6 to 8 minutes. Swirl in a drop or two of yellow food coloring, then pour syrup into a glass measuring cup.

7. Working quickly, pour lengths of syrup (each between 1 and 3 inches long) onto prepared sheets, dragging the tip of a knife through in random places to create flame shapes. If desired, add a drop of red food coloring to the last few tablespoons of syrup to create redder flames. Let stand until hardened, about 5 minutes.

8. Assembly: Place one cake layer on a stand, trimmed-side up, and spread 1 1/2 cups buttercream evenly over surface. Top with remaining cake layer, trimmed-side down. Spread a thin layer of buttercream over top and sides. Refrigerate until firm, about 30 minutes (this ensures a crumb-free finish). Spread remaining frosting evenly over top and sides of cake, keeping top as flat and level as possible.

9. Ganache: Place chocolate in a small heatproof bowl; add salt. Bring cream just to a boil over medium-high heat. Pour over chocolate. Let stand 10 minutes, then whisk until smooth and shiny. Let cool a few minutes. Pour half of warm ganache over center of cake, then slowly but steadily pour remaining ganache around edges, allowing it to drip down sides. Refrigerate until set, about 1 hour. (At this point, cake can be refrigerated up to 1 day; bring to room temperature before serving.)

10. To garnish, press candy flames into top of cake, arranging lighter flames toward back and darker flames toward front.

Cook's Notes

The cake, buttercream, and flames can all be made a day in advance and kept covered at room temperature. The buttercream can also be refrigerated for up to three days, or frozen for up to three months (bring to room temperature and beat again for a minute or two before using).