Amazing cake for chocolate lovers

Ingredients

FOR THE CAKE

Unsalted butter, room temperature, for pans
3 cups all-purpose flour, plus more for pans
3 cups granulated sugar
1 1/2 cups unsweetened Dutch-process cocoa powder
1 tablepoon baking soda
1 1/2 teaspoons baking powder
Coarse salt
4 large eggs
1 1/2 cups low-fat buttermilk
1/2 cup plus 2 tablespoons safflower oil
2 teaspoons pure vanilla extract

FOR THE CARAMEL

4 cups granulated sugar
1/4 cup light corn syrup
2 cups heavy cream
Coarse salt
2 sticks cold unsalted butter, cut into tablespoons
Candy thermometer (very helpful to get your caramel just right)

FOR THE FROSTING

1/4 cup plus 2 tablespoons Dutch-process cocoa powder
2 sticks unsalted butter, room temperature
1/2 cup confectioners sugar
Coarse salt
1 pound semisweet chocolate, chopped, melted, and cooled
Garnish: flaked sea salt

Directions

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 3 pans. Bake until cakes are set and a toothpick inserted into the center of each comes out clean, about 35 minutes. Let cool in pans set on a wire rack for 15 minutes.
8. Turn out cakes onto racks, and let cool completely.
9. Make the caramel: Combine granulated sugar, corn syrup, and 1/4 cup water in a medium saucepan over high heat. Cook, without stirring, until mixture is dark amber, about 10-15 minutes.
10. Remove from heat, and carefully pour in cream; stir until smooth.
11. Return to heat, and cook until a candy thermometer reaches 238 degrees, about 2 minutes.
12. Pour caramel into a medium bowl, stir in 1 teaspoon coarse salt, and let cool slightly, about 15 minutes. Stir in butter, 1 tablespoon at a time. Let cool completely.
13. Meanwhile, make the frosting: Whisk together cocoa and 1/4 cup plus 2 tablespoons warm water in a bowl until cocoa dissolves. 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. Gradually beat in melted chocolate and then cocoa mixture until combined. Let stand for 30 minutes before using.
14. Assembly: Trim tops of cakes using a serrated knife to create a level surface. Cut each in half horizontally to form 2 layers. Transfer 1 layer to a serving platter, and spread 3/4 cup caramel over top. Top with another cake layer, and repeat with remaining caramel and cake layers, leaving top uncovered. Refrigerate until set, about 1 hour.
15. Frost top and sides of cake in a swirling motion. Sprinkle with sea salt.