In a metal mixing bowl that is clean, (no grease or residue or the meringue won't whip) Add egg whites and sugar and whisk together.

Boil a pot of water and place bowl on top of water, whisk mixture until the sugar begins to melt and dissolve and egg whites begin to heat up, you can check for this by sticking your fingers into the mixture and feeling it between the two fingers for any sugar crystals and I do mean any, if they are in there you will feel the crunch in your frosting. I also lick my finger to double check I didn't miss any undissolved sugar crystals.

Once dissolved, use an electric whisk or mixing bowl attachment to beat mixture for 10 -15 minutes, it will look fluffy and meringue like and it will cool down to room temperature.

Add your slightly cooler than room temperature butter to the bowl in chunks until it is all added.

Add your vanilla, cocoa powder, instant espresso and salt and blend until smooth.

If the frosting is still slightly runny and doesn't hold firm peaks, that is fine, place in the refrigerator for 10-20 minutes before using as an icing and it will firm up, you can also whip it again after refrigerating or use it straight from that point.