This is the birthday cake to rule all birthday cakes (and it's not even my birthday). It's deliciously moist, rich, and will satisfy even the strongest chocolate cravings. I'm going to be honest with you: the recipe is a process. But don't be discouraged, I'll break it down for you. You'll learn to make Swiss buttercream (made with egg whites + granulated sugar), and believe me, this is the frosting that will take your cake game to the next level and have everyone asking you "wait, did Martha Stewart make this?

Ingredients

Chocolate Layer Cake

Hot Coffee: 1 1/2 cups
Bittersweet Chocolate: 3 ounces
Flour: 2 1/2 cups
Sugar: 3 cups
Unsweetened Cocoa Powder: 1 1/2 cups
Baking Powder: 3/4 teaspoon
Baking Soda: 2 teaspoons
Salt: 1 1/4 teaspoons
Eggs: 3
Vegetable Oil: 3/4 cup
Buttermilk: 1 1/2 cups
Vanilla: 1 teaspoon

Salted Caramel Buttercream

Sugar: 1 3/4 cups
Water: 1/4 cup
Heavy Cream: 1/2 cup
Butter: 27 tablespoons (really)
Salt: 1 teaspoon
Vanilla: 1 teaspoon
Egg Whites: 4

The How To (Chocolate Cake):

Preheat oven to 300 degrees F
Line bottoms of three 9-inch cake pans with circles of parchment paper - butter the parchment paper
Finely chop the chocolate. In a small bowl, whisk it into the hot coffee until melted and smooth
In a large mixing bowl, whisk together the dry ingredients (sugar, flour, cocoa powder, baking powder, baking soda, and salt)
In the bowl of a stand mixer, beat the eggs on medium speed until thickened and lemon-colored (2-3 minutes)
Pour in oil, buttermilk, vanilla, and coffee/chocolate mixture and beat well
Add dry ingredient mixture and beat on medium speed until combined
Divide batter between three pans and bake at 300 degrees for 35-40 minutes, until a tester inserted in center of cake comes out non-gooey
Cool layers completely in the pans on a wire rack
Run a knife around the edges of pans. Turn the layers out onto the wire rack and remove parchment paper

The How To (Salted Caramel Buttercream):

While the cakes are baking, start your buttercream
In a big, heavy bottomed pot, heat 1 cup sugar and 1/4 cup water over medium high heat
Cook the mixture over medium high heat until the sugar dissolves and it turns a dark amber color (this will take awhile, be patient!)
Remove from heat and whisk in cream, 1 tablespoon butter, 1 teaspoon salt, and 1/2 teaspoon vanilla. Whisk until smooth
Fill a large bowl with ice water. Pour the caramel into a small bowl, and place that bowl into the larger bowl of ice water to cool (make sure not to get any water in the caramel)
Heat a large pot of water until simmering. Place a metal bowl over the simmering water (making sure the water doesn't actually touch the bowl). Whisk 4 egg whites and 3/4 cup sugar over simmering water until you can't feel the sugar if you rub it between your finger tips.
Transfer the egg white mixture to the bowl of a stand mixer. Using the whisk attachment, beat on medium high speed until mixture turns white, doubles in size, and soft peaks form.
Add 26 tablespoons (3 sticks + 2 tablespoons) butter, one stick at a time.
Whip until very fluffy, about 5 minutes.
Pour salted caramel into buttercream, along with another 1/2 teaspoon vanilla and beat until combined.

The How To (Assembly):

Trim any domed tops of the layers with a serrated knife.
Alternate cake and frosting layers
Coat cake in a very thin "crumb layer" of frosting, place in the fridge (or in my case, in my very cold backyard) for 15 minutes. This tutorial from Oh Happy Day is really, really helpful when you're learning how to frost + decorate a layer cake.
Remove from fridge and frost the rest of the cake - you're looking for a thick-ish, pillowy layer
Add candles
Sing happy birthday

A Few Notes:

Don't have any coffee on hand? Use stout! I've made this cake with Guinness many times, and it produces an equally delicious and moist result (bonus: you can drink the leftovers)
Don't worry if you only have two cake pans - reserve the last third of batter and bake it in a second wave while the other two layers are cooling on the wire rack
The original recipe says to bake this cake in two 10x2 inch cake pans but I find that most people don't have that size laying around! If you do and would like to use them instead, all you'll need to do is increase the baking time to 1 hour-1 hour ten minutes
Don't attempt to turn the layers out onto the wire racks before they're cool. Nobody likes crumbly cake (OK everyone still likes crumbly cake, but trust me)
If you're not feeling the salted caramel today, skip the caramel step! Add 1 teaspoon of vanilla to the buttercream base and you're done