Preheat your oven to 225°F (110°C) and line a baking sheet with parchment paper.
In a large mixing bowl, use an electric mixer to beat the egg whites until they become frothy.
Add the cream of tartar and pinch of salt, continuing to beat until soft peaks form.
Gradually add the granulated sugar, about a tablespoon at a time, while continuing to beat the mixture until glossy stiff peaks form (around 5-7 minutes).
Gently fold in the instant coffee granules, cocoa powder, and vanilla extract using a spatula, being careful not to deflate the egg whites.
Transfer the meringue mixture to a piping bag fitted with a large round or star tip. Pipe small mounds or swirls onto the prepared baking sheet, spacing them about an inch apart.
Bake the cookies in the preheated oven for about 1.5 to 2 hours, or until they are completely dry and can easily lift off the parchment paper.
Turn off the oven and let the cookies cool inside with the door slightly ajar for an hour. This will help them dry out further and prevent cracking.
Once cooled, serve the mocha meringue cookies as is, or dust with cocoa powder or sprinkle with chocolate shavings for a decorative touch.
Notes
Allow cookies to cool in the oven to prevent cracking.