Pre-heat the oven to 350ºF.

Grease and line the bottom of 3 8-inch cake pans with a circle of parchment paper. Grease the parchment and the sides of the pan as well.

In a medium saucepan, bring the stout and butter to a boil over medium-heat. Don’t let it boil. As soon as the butter melts, turn the heat off.

Add sifted cocoa powder to mixture and whisk until smooth.

Set aside to cool slightly.

Meanwhile, sift together the flour, baking soda, sea salt. Set aside.

In a large mixing bowl, whisk the eggs for 30 seconds. Add the sugar to the eggs and whisk until the mixture is lightened in color—about 2 minutes.

Add the sour cream and whisk until smooth.

Add the cooled down stout/butter/cocoa mixture to egg mixture.

Whisk until combined.

Add the vanilla extract and mix.

Add the dry ingredient mixture to the bowl. Fold with a spatula to combine.

Once combined, add the hot coffee to the batter, whisk until incorporated, and it has no lumps.

Divide the batter between the prepared pans.

Bake for about 25-30 minutes, rotating in between, and until a toothpick comes out clean when inserted in the cake.

Remove the cakes from the oven. Let them cool for 10 minutes. Transfer the cakes to a wire rack to cool down.

Place the sugar in a medium heavy-bottom saucepan over medium heat. Cook the sugar, stirring frequently to melt evenly. Continue cooking until it’s fully melted and turns a deep amber color. When this happens, move quickly because the sugar can turn burnt and bitter really fast.

Add the heavy cream to the pan. Be careful, it will bubble up vigorously and you must protect your hand and face so you don’t get burnt.

Once it subsides, stir quickly.

Add the butter carefully. The mixture will bubble up again. Whisk until completely melted and smooth

Add the stout and kosher salt, and whisk to incorporate. Let the caramel simmer for 1 minute, until slightly thickened.

Remove from the heat and pour into a bowl or jar. The sauce will thicken more as it cools. Let it cool down completely before adding to the buttercream or using as cake filling.

Make ahead tip: you can make this caramel even up to 10 days ahead of time. Keep it in the fridge. When it’s time to use it in the recipe, remove from the fridge about 1 hour before using it. Or you can gently microwave for 5-10 seconds at a time, stirring constantly, until it’s smooth. Don’t overdo it, or it can become too hot and you’ll have to wait to add it to the buttercream.

Remove butter from the fridge about 20 minutes before making the frosting. We are looking for the perfect butter temperature—around 72°F. This is very important when making Swiss Meringue Buttercream. If the butter is too cold, it forms lumps in the buttercream, and if it’s too soft, the buttercream becomes soupy.

In a heatproof bowl, combine the egg whites and granulated sugar. Place the bowl over a saucepan with a few inches of simmering water, making sure the bottom of the bowl doesn’t touch the water. Whisk constantly until the sugar is fully dissolved and the mixture reaches 160°F (71°C). It should feel completely smooth when rubbed between your fingers.

Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium-high speed until stiff, glossy peaks form and the bowl is no longer warm to the touch. This can take 8–12 minutes. Make sure the peaks are stiff. If the peaks are soft, the buttercream will turn out soupy.

Switch to the paddle attachment and, with the mixer on medium speed, add the softened butter a few tablespoons at a time, letting each addition incorporate before adding more. Continue mixing until all the butter is added. The buttercream may look curdled or soupy at some point — keep mixing and it will come together into a smooth, creamy consistency.

Add the stout caramel sauce and the vanilla extract and beat until fully incorporated.

If the buttercream looks separated or chunky at this point, turn the speed to low and mix for about 5 to 10 minutes on the lowest setting. It will help the buttercream become creamy and smooth.

Use immediately, or refrigerate until ready to use. Bring back to room temperature and rewhip before frosting.

Place one cooled cake layer on a cake board or serving plate.

Spread an even layer of Salted Caramel Swiss Meringue Buttercream over the top. Transfer some buttercream to a piping bag and pipe a thick border around the edge of the cake to create a dam. Fill the center with a generous layer of stout caramel sauce and spread gently.

Refrigerate the cake for 20–30 minutes, until the frosting is firm to the touch.

Place the chopped chocolate in a bowl. Heat up the heavy cream until hot.

Pour over the chocolate. Whisk until the chocolate has melted entirely. If there are pieces of chocolate that didn’t melt, place the bowl in the microwave for a few seconds, until the chocolate has melted entirely.

Let the ganache cool down for about 10 to 15 minutes before pouring on top of the cake.

You can use a spoon to do this, or a piping bag. I like to place the ganache in a piping bag, and snip just a small hole with scissors. Then, test on the cake, drip just one drop along the edge of the cake, and watch how it drips, if it stays still, or if it drips too fast. If it drips too fast, and too thin, you can place the ganache in the fridge for 3 to 5 minutes, stir it, and try again. And if it stays still and doesn’t drip at all, you can microwave the ganache for 3 to 5 seconds, and stir, and test again.

When the ganache is thick, but not too thick that won’t drip, you can go around the cake, dripping it off the edges.

Then pour the ganache on top of the cake. Use a spatula to smooth it out.

Place the cake in the fridge for 20 minutes so the ganache has a chance to set.

Transfer remaining buttercream to a piping bag fitted with a 1M star tip and pipe swirls on top of the cake. Drizzle extra caramel sauce if desired and finish with a sprinkle of flaky sea salt.

Slice and serve.

Store the cake in the fridge for up to 4 days. You can freeze the cake, or cake slices, for up to 1 month.