It's worth making homemade raspberry syrup for this cocktail. You can always substitute bought syrup but something of the freshness will be lost.
Shake all the ingredients vigorously in a shaker without ice to emulsify the egg white.
Add ice and shake again.
Double strain into a coupe or cocktail glass.
Garnish with fresh raspberries.
I've fiddled about with the quantities a little. The IBA (International Bartenders Association) lists the quantity of lemon juice as 15ml. I like my cocktails to be a little sweet so found this measure to be quite tart and mouth-puckeringly so.
Play with the quantities until you find a balance between the sweet fruitiness of the raspberry and the tartness of the lemon juice. You won't be disappointed.