Perfect Chocolate Swiss Meringue Buttercream

1. Prep all the bowls, whisks, spatulas by making sure they are clean and dry. Make sure there is no fat residue on the bowls and whisks as well.

Melting the chocolate

1. Place a pot on the stove over medium heat and add about 1 - 2 inches of water. Cover and bring the water to a simmer.
2. Add bittersweet chocolate into a metal or heatproof bowl, and place the bowl over the simmering pot of water. This will act as a double boiler to melt the chocolate.
3. Be careful not to let ANY WATER get into the chocolate as this will seize the chocolate.
4. Melt the chocolate over the simmering water. Once melted, set aside. Let it cool down, but still be liquid.

Preparing the meringue base

1. Place the egg whites in the clean, dry mixing bowl from your stand mixer, or a different metal bowl. Add the sugar and salt, and whisk to combine.
2. Place the bowl over the simmering pot of water and stir the egg white and sugar mixture continuously with a hand whisk, while heating. Heat until the sugar is completely dissolved.
3. Keep heating the mixture until it registers between 166 - 175°F (74.5 - 79.5°C).
4. Remove from the heat and keep mixing/whisking the egg mixture to cool it down slightly, while making sure that any sugar crystals on the sides of the bowl completely melt back into the mixture.
5. Place the mixing bowl in the stand mixer (or transfer the egg white mixture into the mixing bowl).
6. With a whisk attachment, whisk the egg sugar mixture on high speed (start on low and slowly increase speed to avoid spillage), until you form a meringue. Keep whisking until you reach stiff peaks. If there is any fat residue on any item that makes contact with the egg whites, the meringue will not reach stiff peaks.
7. Feel the sides of the bowl to make sure the meringue mixture is cooling down to almost room temperature (between 80 - 90°F / 27 - 32°C). If you don’t have a thermometer, the bowl should no longer feel warm to the touch.
8. Once the right temperature is reached, start adding the unsalted butter cubes.

Adding butter and chocolate

1. Switch from the whisk attachment to the paddle attachment.
2. Add the butter, one portion at a time, into the meringue base, and mix on medium high speed.
3. Mix well between butter additions, making sure each butter portion mixes in well before adding the next portion. If you feel the butter is dissolving into the buttercream too quickly, slow down and take your time mixing the buttercream between additions. This will help cool down the buttercream base, preventing it from turning too soupy.
4. On the other hand, if your buttercream turns into a cottage cheese-like consistency (looks curdled), don’t worry. Just keep mixing and adding any leftover butter, and it should become creamy. Remember to scrape down the sides of the bowl as you mix to ensure all the meringue is mixing in properly.
5. Once all the butter is added and the buttercream is nice and creamy, add the flavoring. If you're using instant coffee, dissolve it in the vanilla extract and add that into the buttercream.
6. Reduce the mixer speed to medium - low speed and gently stream in the melted but cooled bittersweet chocolate. Once the chocolate is added, stop the mixer and scrape down the sides of the bowl (to get any chocolate splashed on the sides). Mix on medium or medium high speed until all the chocolate has mixed in properly and you have a creamy chocolate buttercream.
7. If the buttercream is too soft, place the mixing bowl in the fridge for about 10 minutes at a time, and mix until it reaches the right consistency and temperature (about 70 - 73°F / 21 - 22.7°C).
8. The buttercream is now ready to be used.