Vegan Coffee Buttercream (Swiss Meringue Buttercream)

1. Mix together the instant coffee and boiling water and set aside to cool. 2. Add the aquafaba and sugar to a large bowl and place the bowl on top of a saucepan with a few inches of water in the bottom - this is known as a bain-marie (water bath). Bring the temperature up to medium and allow the mixture to heat for a few minutes until the sugar is dissolved. 3. Remove the bowl from the heat and use an electric whisk (or transfer the syrup into your stand mixer) and beat on high speed for 15-20 minutes until the mixture is completely cooled and glossy. The mixture should be stiff and glossy and should stay in the bowl if you turn it upside down (carefully!). 4. Start slowly adding the chunks of butter to the meringue, one at a time, allowing the mixture to incorporate for about 5 seconds between each one. The mixture will flatten as you add the butter, just continue to add the butter as it will stiffen when the full amount of butter is incorporated. 5. Once all the butter has been added the mixture be thick like buttercream, continue to whisk on low for 5-10 minutes until the mixture is fluffy and lightened in color. If the mixture looks split, don't worry it will come together with enough blending. 6. Lastly, add the cooled coffee mixture to the buttercream and continue to whisk for a couple of minutes until combined. 7. You can store this coffee buttercream in an airtight container in the fridge. It will harden when chilled, so before use, allow it to come to room temperature until it comes back to a creamy consistency.