In the bowl of a stand mixer (I think a hand mixer will work too, it will just take ages but I've never tried it), add in the egg whites, sugar, and salt. Whisk to combine.
Place a medium sauce pot half way full with water onto the stove. Bring the water to a simmer.
Set the mixing bowl with the egg whites and sugar over the bowl of simmering water and turn the heat to low. The water shouldn’t touch the bottom of the mixing bowl.
Whisk the egg whites and sugar constantly until the sugar has fully dissolved into the egg whites. To check and see if the sugar has dissolved, pinch and rub some of the mixture in between your fingers and feel if you still feel any of the sugar granules, if not you’re good to go. If you do just keep cooking a bit longer.
Once the sugar has dissolved, turn off the heat and remove the bowl from the water. Leave it to cool off for about 10 minutes.Using your mixer, whip the egg white mixture first on medium and then on high speed until fluffy, shiny and stiff.
Turn off the mixer and if you have it, use a kitchen blow torch to completely torch the surface of the meringue.
Whip again until completely mixed, then repeat the torching 3 more times.
The bottom of the bowl should have cooled off at this point but if not, place the bowl in the fridge for 5 minutes.
Once cool to the touch, turn the mixer to medium high speed and add in 1″ blocks of butter at a time whipping until all of the butter has mixed in. It will deflate a little bit at the beginning, that’s ok! Also it may start to look split or runny at some point, don’t stress just put the bowl back in the fridge to cool down for a bit and then keep whipping and adding in the butter.
When almost all of the butter has been added, the mixture is going to look funny, just keep whipping and it will smooth out.
Once all of the butter has been added, take the bowl from the mixer and scrape down the edges. Pour in the espresso powder and vanilla bean paste and whip again on medium high until just combined. While the mixer is running slowly pour in the cold heavy cream and whip until combined.
Take the chilled cake out of the fridge, remove the cake collar and acetate ring. Frost the cake however you want! I piped the cake with the extra frosting and topped it with a simple chocolate ganache and cut pears.
Serve immediately or within the hour. Otherwise place the cake back in the fridge until 30 minutes before you plan to serve.