To make the simple syrup, add all the ingredients to a small saucepan. Place on a low heat (no need to stir) until it reaches a boil, then turn off and let it cool to room temperature. Strain into a jug – for easier pouring – using a sieve and piece of muslin cloth.
For the cocktails, start by adding your lemon juice, gin, egg white and simple syrup to a cocktail shaker (no ice yet!!). Shake for around 20-30 seconds, until the egg is emulsified and mixture goes all creamy
Add a handful of ice cubes and shake again for around 20 seconds or until the mixture is cold (the outside of the shaker will start to frost up)
Strain into martini (or other) glasses and top with prosecco, pouring slowly to avoid everything fizzing everywhere
Garnish with a slice of dried lemon or fresh lemon thyme (I wouldn’t recommend tea or lemon myrtle flakes, as no one want to have to spit that out!)