Salted Caramel "Ding Dong" Cake

Ingredients

• 1 teaspoon double-acting baking powder 
• 1 teaspoon baking soda 
• 9 ounces bittersweet chocolate chopped
• 0.8 cup buttermilk 
• 2 cups cake flour 
• 1 cup cocoa powder unsweetened
• 3 large eggs 
• 1.3 teaspoons gelatin powder unflavored
• 1.5 cups cup heavy whipping cream chilled
• 1.1 teaspoons kosher salt 
• 0.5 cup powdered sugar 
• 12 servings sea salt (such as Maldon)
• 1 cup strong coffee decoction hot
• 1 cup sugar 
• 1 cup butter unsalted room temperature (2 sticks)
• 1  vanilla pod split
• 1 teaspoon vanilla extract 

Equipment

• bowl
• frying pan
• baking sheet
• sauce pan
• oven
• knife
• whisk
• wire rack
• hand mixer
• microwave
• springform pan
• offset spatula
• serrated knife
• pastry brush

Directions

1. Preheat oven to 350°F. Coat cake panswith nonstick spray. Line bottom of panswith parchment-paper rounds; coat paper.
2. Place cocoa powder and chocolate in amedium metal bowl.
3. Pour hot coffee over.
4. Let stand for 1 minute. Stir until smooth. Stirin buttermilk and vanilla; set aside.
5. Whisk cake flour and next 3 ingredientsin a medium bowl. Using an electric mixer,beat sugar and butter in a large bowl untillight and fluffy, about 4 minutes.
6. Add eggsone at a time, beating to blend betweenadditions and occasionally scrapingdown sides and bottom of bowl. Beat untillight and fluffy, about 4 minutes.
7. Add dryingredients in 3 additions, alternating withchocolate mixture in 2 additions, beginningand ending with dry ingredients. Dividebatter evenly between pans; smooth tops.
8. Bake cakes until a tester inserted into thecenters comes out clean, about 35 minutes.
9. Transfer to wire racks; let cakes cool in pansfor 10 minutes (cakes will deflate slightly).Run a knife around pans to loosen cakes;invert cakes onto racks. Peel off paper andlet cakes cool completely. Turn cakes over.
10. If needed, use a long serrated knife to cutoff bumps or trim dome from top of eachcake to create a flat, even surface.
11. Place chocolate andsalt in a medium bowl. Stir sugar and 1/4 cupwater in a medium deep saucepan overmedium-low heat until sugar dissolves.Increase heat and cook without stirring,occasionally swirling pan and brushingdown sides with a wet pastry brush, untilsugar is deep amber, about 9 minutes.
12. Remove from heat and gradually add cream(mixture will bubble vigorously). Stir overmedium heat until caramel bits dissolve.
13. Pour over chocolate in bowl.
14. Add vanilla; stiruntil mixture is smooth.
15. Let cool slightly.
16. Place 1 cake layer in springform pan.
17. Pour1 cup ganache over. Chill until set, about30 minutes. Cover remaining ganache andlet stand at room temperature.
18. Place 2 tablespoons coldwater in a small heatproof glass or metalbowl.
19. Sprinkle gelatin over; let stand untilgelatin softens, about 10 minutes.
20. Pour water to a depth of 1/2" into a smallskillet set over medium heat.
21. Transfer bowlwith gelatin to skillet; stir until gelatindissolves, about 2 minutes.
22. Remove bowlfrom skillet. Set aside.
23. Place cream and powdered sugar in alarge bowl. Scrape in seeds from vanillabean. Using an electric mixer, beat creamuntil soft peaks form.
24. Add gelatin; beatfilling until firm peaks form.
25. Spoon filling over chilled ganache oncake layer in pan; smooth top. Gently placesecond cake layer on top. Cover tightly withplastic wrap and chill until cream layer isset, at least 6 hours or overnight.
26. Remove sides from springform pan.Using a knife or offset spatula, scrape offany filling that may have leaked out frombetween cakes to form smooth sides.
27. Transfer cake to a wire rack set inside arimmed baking sheet.
28. Rewarm remaining ganache until justpourable. (Microwave in a microwave-safebowl, or set a metal bowl over a largesaucepan of simmering water until justwarm, not hot.)
29. Pour ganache over cake,tilting cake as needed to allow ganache todrip down sides and using an offset spatulato help spread ganache, if needed, to coversides of cake. Chill until ganache is set,about 1 hour. DO AHEAD: Cake can be made2 days ahead. Cover with a cake dome; chill.
30. Let stand at room temperature for 1 hourbefore serving.
31. Sprinkle cake with flaky sea salt.