-
1
Preheat oven to 350 degrees.
-
2
Make the cake: Butter three 9-inch round cake pans, and dust with flour, tapping out excess.
-
3
Sift flour, granulated sugar, cocoa, baking soda, baking powder, and 1 1/2 teaspoons course salt into the bowl of a mixer.
-
4
Beat on low speed until just combined.
-
5
Raise speed to medium, and add eggs, buttermilk, 1 1/2 cups warm water, oil, and vanilla.
-
6
Beat until smooth, about 3 minutes.
-
7
Divide batter among pans.
-
8
Bake until cakes are set and a toothpick inserted into the center of each comes out clean, about 35 minutes.
-
9
Let cool in pans set on a wire rack for 15 minutes.
-
10
Turn out cakes onto racks, and let cool completely.
-
11
Make the caramel: Combine granulated sugar, corn syrup, and 1/4 cup water in a medium saucepan over high heat.
-
12
Cook, without stirring, until mixture is dark amber, about 14 minutes.
-
13
Remove from heat, and carefully pour in cream (mixture will spatter); stir until smooth.
-
14
Return to heat, and cook until a candy thermometer reaches 238 degrees, about 2 minutes.
-
15
Pour caramel into a medium bowl, stir in 1 teaspoon coarse salt, and let cool slightly, about 15 minutes.
-
16
Stir in butter, 1 tablespoon at a time.
-
17
Let cool completely.
-
18
Meanwhile, make the frosting: Whisk together cocoa and 1/4 cup plus 2 tablespoons warm water in a bowl until cocoa dissolves.
-
19
Beat butter, confectioners' sugar, and a generous pinch of coarse salt in a clean bowl with a mixer on medium speed until pale and fluffy.
-
20
Gradually beat in melted chocolate and then cocoa mixture until combined.
-
21
Let stand for 30 minutes before using.
-
22
Trim tops of cakes using a serrated knife to create a level surface.
-
23
Cut each in half horizontally to form 2 layers.
-
24
Transfer 1 layer to a serving platter, and spread 3/4 cup caramel over top.
-
25
Top with another cake layer, and repeat with remaining caramel and cake layers, leaving top uncovered.
-
26
Refrigerate until set, about 1 hour.
-
27
Frost top and sides of cake in a swirling motion.
