(per 2 drinks)
4 oz genever (grey-bottle Bols)
1 oz maraschino liqueur (Luxardo, obviously)
1 1/2 oz blackberry syrup (homemade)
Juice of 1 lemon
White of 1 egg
Shake all of the above vigorously over large cold ice cubes, strain into chilled fizz glasses and top up with 2-3 oz of soda water each. Garnish with a lemon twist, if you like.