First, make the sugar syrup: Place a pot on the stovetop and pour in water, sugar, and syrup.
Bring it to a boil and let it reach 115 degrees Celsius (239 degrees Fahrenheit) while stirring. It is necessary to use a sugar thermometer and it requires a lot of patience - it takes a little time.
Pour the egg whites and sugar into a bowl and whisk them with a hand mixer/on a stand mixer.
When the sugar syrup has reached 121 degrees Celsius (250 degrees Fahrenheit), remove it and slowly pour it into the bowl with the egg whites and sugar.
Continue whisking until the mixture has cooled down, which takes up to 10-15 minutes.
Afterwards, your Italian meringue is ready to use!