Chill a Collins glass with ice and water and set aside.
Add the gin, blue curaçao, lemon juice, simple syrup and egg white into a shaker, and dry-shake (without ice) vigorously.
Add ice and shake again until well-chilled.
Discard ice from the prepared glass, then strain the contents of the shaker into the glass.
Top with tonic water and orange blossom water.
