Chill a coupe or flute by placing it in the freezer or filling with ice water while you work. In a cocktail shaker, add the gin, fresh lemon juice, elderflower liqueur, simple syrup, and egg white if using.

Dry shake

Without ice, seal the shaker and shake vigorously for 12–15 seconds to emulsify the egg white and create a silky texture.

Wet shake

Open the shaker, add 3–4 large ice cubes, reseal and shake hard for another 10–12 seconds until the shaker is well chilled and slightly frosty on the outside.

Sparkle & Finish

Strain and top

Discard the ice or water from the chilled glass. Double-strain the shaken mixture into the chilled coupe or flute using a fine-mesh strainer to remove ice shards and any coalesced egg bits. Gently top with 2 oz (about) chilled Prosecco or dry sparkling wine poured slowly down the side so it mixes but retains a light head.

Bitters and garnish

Add 2 dashes of orange bitters on the foam (if egg white used) or into the surface, then express a lemon twist over the cocktail to release oils and drop it in. Optionally float an edible flower or a small mint sprig for visual appeal.

Serve

Serve immediately while the drink is chilled and effervescent. Encourage the diner to sip to enjoy the layered floral, citrus, and sparkling flavors.