Preheat oven to 325°. Butter or spray the inside of 2, 9-inch cake pans with nonstick cooking spray. Line with a parchment circle on the bottom of each.

Combine cocoa, chocolate and espresso powder in a large mixing bowl. Bring Guinness to just barely boiling in a small saucepan. Pour hot Guinness over chocolate mixture and whisk until completely melted and smooth. Set aside to cool to room temperature.

While the chocolate is cooling, combine flour, salt, and baking soda together in a small bowl and whisk.

When chocolate is cool, whisk in the sour cream. You could also play God and cool the chocolate by adding cold sour cream, but that is your choice.

Beat the butter, sugar and vanilla together on medium speed in a large bowl with an electric mixer or stand mixer fitted with the paddle attachment until pale and fluffy. Beat in the eggs, one at a time, until incorporated. The batter may seem separated and that is okay!

Reduce the mixer speed to low and alternately add the flour mixture and the chocolate mixture in three additions, beginning and ending with flour.

Divide the cake batter between prepared cake pans. Bake until a toothpick or cake tester comes out with some crumbs still attached; 30-35 minutes.

Let the cakes cool 10 minutes in the pan then run a paring knife or small offset spatula around the edges and turn out on a wire rack to cool completely.

While the cakes cool, prepare the frosting.

In a large heat-proof bowl, add chopped chocolate, vanilla extract, and salt.

Note: Due to the total amount of heavy cream in this recipe, I recommend chopping the chocolate even if you are using chocolate pieces. The cream might cool faster than it can melt the chocolate. I had to microwave on 50% power in 10 second intervals to finish melting the chocolate in my ganache. This is not best practice!

In a small saucepan bring whipping cream just to a boil. Pour over chocolate, shake to distribute and cover the chocolate.

Allow to sit for 2 minutes.

Slowly whisk starting from the center and working your way out to create an emulsion.

Sift in the cocoa powder, whisk to incorporate. You can also put it in before the cream but it has a tendency to clump and create lumps that will not come out. You risk breaking the emulsion by whisking enough to smooth them out.

Add butter to the still hot ganache. Switch to a silicone spatula and gently stir in one direction until all the butter has melted and incorporated into the ganache.

Stir in the salted caramel sauce. I used 1 cup, but you can add to taste if preferred.

Cover the surface with plastic and allow to cool to room temperature. You can speed it up by putting it in the fridge and stirring every 10 minutes. I recommend doing this if your room is warm. Mine was about 70°F, so it cooled to room temperature in a little under 2 hours. At 70°F the fudge frosting will hold beautiful lines.

Place one layer of cake on your favorite cake plate or cake stand. Add about 1 cup cooled frosting on the top and spread out into an even layer.

Add the second cooled cake layer on top. Add another cup of frosting on the top, spreading it out and allowing to extend over the edges. Using an offset or straight metal cake spatula, add a nice layer of frosting to the sides of the cake. Add additional frosting to the top and swirl as desired.

Serve room temperature or cover and refrigerate for up to 3 days. The cake will gradually lose moisture, so I love to make it the day before or the same day it will be served. You can also make the cake layers, cool, wrap tightly in plastic wrap and freeze for 1 month before assembling. Allow the cake to come to room temperature for the optimal texture.