Combine gin, grenadine, heavy cream, milk, and egg white in a cocktail shaker without ice.
Dry shake vigorously for 15 seconds to emulsify the egg white and cream.
Add a full scoop of ice and shake hard for 10–12 seconds until well chilled.
Double-strain through a fine mesh strainer into a chilled martini glass.
Serve immediately and allow the foam to settle and rise to the surface.
Using both heavy cream and milk keeps the mouthfeel rich but not cloying - the fat content of the cream binds with the egg white during the dry shake to produce a particularly stable, velvety foam. Make sure your grenadine is pomegranate-based, not artificially flavored, to keep the floral notes honest.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Ace.