Chocolate and Salted Caramel Cake

Method

1. 1
   Preheat oven to 350°F/175°C. Line 3 8-inch cake pans with parchment paper rounds and spray the sides of the pans with non-stick cooking spray or baking spray. If you don't have 3 cake pans, the batter can sit at room temperature while the first layer(s) bake. Bake as many layers at a time as you can.
2. 2
   Sift or whisk together 2 cups flour, 2 cups granulated sugar, 3/4 cup cocoa powder, 2 tsp baking powder, 1 1/2 tsp baking soda, 1 tsp fine salt, and 1 tsp instant espresso or coffee (optional) in a large bowl. Set aside.
3. 3
   In a separate, large bowl, add 1 cup warm water, 1 cup buttermilk, 1/2 cup oil, 2 eggs, and 1 tsp vanilla and whisk together until fully incorporated.
4. 4
   Whisk the dry ingredients into the wet ingredients until they're just combined, and the batter is smooth.
5. 5
   Divide the batter evenly between the prepared cake pans (about 475g per pan if you're making 3 layers) and bake for 23-25 minutes or until a toothpick comes out with a few moist crumbs.
6. 6
   Let the pans cool for 10 minutes, then run a small offset spatula around the perimeter of the pan to separate the cake from the pan.
7. 7
   Place the cake pans into the freezer for 30 minutes to accelerate the cooling process. This helps lock in the steam and makes the layers extra moist. If you don't have room in the freezer, place the cake pans on a wire rack and let them cool fully before removing them.
8. 8
   Once the layers are fully cooled, carefully flip the pans and remove the layers. These cake layers bake up pretty flat, so leveling them is optional, but I like to level them with a serrated knife to make the cake easier to fill and frost.
9. 9
   If you make these cake layers in advance and freeze them, let them thaw for about 15 minutes before making the cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble the cake.
10. 10
    Make the caramel while the cake layers bake and cool. This can be made up to 2 weeks in advance.
11. 11
    Place a heavy-bottomed saucepan over medium heat. Once the pan has warmed up, pour in 2 cups of sugar gradually, adding 1/4 cup at a time. Stir as needed with a rubber spatula. Wait until the sugar is mostly dissolved, then add in the next bit of sugar. As the sugar melts, it will gradually deepen in color.
12. 12
    Stir occasionally until the sugar is fully dissolved and has become an amber color, then turn off the heat.
13. 13
    Slowly mix in 3/4 cup (1 1/2 sticks) of room temperature butter (2 Tbsp at a time), then stir in 1/2 cup of room temperature heavy cream and 1/2 tsp salt. If these aren't at room temperature, they can cause the sugar to seize and make it more difficult to mix together. Note: sometimes the butter also has a hard time incorporating into the sugar if it's been cooked a bit too long or at too high a heat! If this happens to you, you may want to turn the heat down a bit the next time you make it or use a heavier-bottomed pan that can help the sugar cook more evenly. But don't worry! You can gradually stir the butter into the caramel as it cools, and it should incorporate back together. The mixture will be thin but will thicken as it cools. Pour into a separate container, then set aside to cool.
14. 14
    While the cake layers and caramel cool, make the buttercream frosting. In a large bowl or the bowl of a stand mixer, beat 2 cups of butter on a medium-high speed for 1 minute with a paddle attachment or hand mixer until smooth and fluffy.
15. 15
    Mix in 1 tsp vanilla extract and 1/2 tsp salt on a low speed until the ingredients are incorporated.
16. 16
    Gradually mix in 7 cups of powdered sugar and 1/3 cup of heavy cream on a low speed. Scrape the sides and bottom of the bowl as needed with a rubber spatula. Then mix in 1/2 cup of homemade caramel (made above). Wait to add the melted dark chocolate until the cake has been assembled.
17. 17
    Mix on low until the desired consistency is reached. If the frosting seems too thick, add additional cream (1 Tbsp at a time). If the frosting seems too thin, add in more powdered sugar (1/4 cup at a time).
18. 18
    Place about 1 cup of the caramel buttercream into a large piping bag and cut an opening about 3/4-inch at the base of the bag. Cover the remaining frosting with plastic wrap to prevent crusting and set aside.
19. 19
    When you're ready to assemble the cake, stack and frost the cake layers on a greaseproof cake board or flat plate using a dab of buttercream to help stick the first cake layer to the board.
20. 20
    Spread an even layer of caramel buttercream on top of the cake layer. Then pipe a buttercream ring around the edge and drizzle slightly less than half of the remaining caramel on top of the buttercream (I like to save a little caramel to drizzle on top of the cake). If the caramel has firmed up as it's cooled off, heat it in 10-second intervals in the microwave until it becomes more fluid.
21. 21
    Repeat with the remaining cake layers. Flip the top cake layer upside down to make the cake easier to frost and minimize crumbing.
22. 22
    Once the layers are stacked, chill the cake in the freezer for 20 minutes or in the fridge for 30 minutes to prevent the layers from sliding.
23. 23
    While the cake chills, mix 1 cup of dark chocolate that's been melted and cooled for about 10 minutes into the remaining buttercream.
24. 24
    Remove the cake from the fridge or freezer and cover it in a thick layer of chocolate caramel buttercream. Use a large offset spatula or the back of a spoon to give the frosting a textured look, then drizzle any remaining caramel on top of the cake, add a sprinkle of flaky sea salt, and enjoy.