Pull a double espresso into a tall metal shaker or milk jug.
Add the sugar syrup and two ice cubes.
Whip with a handheld drink mixer or shake extremely hard for 20 seconds, until the volume roughly doubles and a dense foam forms.
Fill a collins glass with ice and pour the whipped espresso over it.
Serve with a straw and no milk.
Standard across Greece and Cyprus, where a freddo espresso and a freddo cappuccino are separate orders and getting them confused marks you out. The handheld frother is what Greek cafés actually use; a cocktail shaker is a workable substitute if you shake harder than feels reasonable.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Freddo Espresso.