Mix the sugar, salt and flavoring if using into the espresso until combined.
Fill a tall glass half full with ice, then pour in the espresso. Top off with the sparkling water. Stir before enjoying.
Recipe Notes
You can use any flavoring you would like; if you’re using a ground spice or an extract, you can add it straight to the drink. For an herb, spice or citrus peel, I would suggest making a simple syrup with 1 part water and 1 part sugar, then adding the flavoring to taste and letting it infuse into the syrup.