Perfect Chocolate Cake

For the cake batter

1. Preheat the oven to 325°F (165°C).

2. Line two 8-inch cake pans with parchment paper and grease with cooking spray.

3. Sift the cake flour, baking powder, kosher salt, and baking soda together into a large bowl.

4. In another bowl, whisk the cocoa powder and boiling water until smooth.

5. Whisk in the sugar, eggs, and neutral oil until combined.

6. Fold the dry ingredients into the wet mixture until just combined.

   Be gentle to avoid gluten development, which can make the cake tough.

7. Whisk in the sour cream, vanilla, and white distilled vinegar.

8. Divide the batter evenly between the prepared cake pans using a kitchen scale.

9. Bake on the middle rack at 325°F (165°C) until a toothpick inserted into the center comes out clean, 50–55 minutes.

   Then 50 min of waiting

10. Cool the cakes completely in the pans on a wire rack.

    Then 60 min of waiting

11. Wrap the cooled cakes and chill in the refrigerator to make them easier to slice.

    Then 60 min of waiting

For the buttercream

12. Whisk the sugar and egg whites together in a heatproof glass bowl set over a pot of simmering water (double boiler).

13. Whisk constantly over heat until the sugar dissolves completely and the mixture feels smooth when rubbed between two fingers, 3–5 minutes.

14. Transfer the bowl to a stand mixer fitted with the whisk attachment and beat on high speed until stiff, glossy peaks form, 8–10 minutes.

15. Reduce the speed and add the room temperature salted butter a few tablespoons at a time, whisking until incorporated.

16. Add the vanilla and melted, cooled milk chocolate, whipping until smooth and silky.

For the glossy chocolate sauce

17. Combine the water, corn syrup, granulated sugar, cocoa powder, vanilla, and salt in a saucepan.

18. Bring to a boil over high heat, whisking constantly to break up any lumps.

19. Simmer until reduced by about a quarter and thick enough to coat the back of a spoon, 8–10 minutes.

20. Remove from heat and allow to cool.

To assemble

21. Trim the rounded tops off the chilled cakes to make them flat.

22. Slice each cake horizontally into two even layers to create four total layers.

23. Place three strips of parchment paper around the edges of a cake stand to keep it clean.

24. Place the first cake layer on the stand and brush liberally with the glossy chocolate sauce.

25. Spread an even layer of buttercream over the cake using an offset spatula.

26. Repeat the process with the remaining cake layers, soaking each layer with sauce and spreading with buttercream.

27. Apply a thin layer of buttercream over the entire top and sides of the cake as a crumb coat.

28. Chill the crumb-coated cake in the refrigerator until firm, about 20 minutes.

    Then 20 min of waiting

29. Frost the cake with the remaining buttercream, creating decorative swooshes.

30. Dust the top with cocoa powder and sprinkle with flaky sea salt.

31. Remove the parchment strips before slicing.

32. Room temperature eggs work best for the cake, though cold eggs straight from the fridge will work if needed.

33. Dip your knife in hot water and wipe it dry between cuts for clean cake slices.