Combine all ingredients except the soda water into the shaker tin, add ice, and shake for about 10-15 seconds.
Double strain from one shaker into the other to remove ice.
Shake again for an additional 15-20 seconds, until well mixed (a reverse dry shake).
Pour without straining into a Collins glass or other tall glass.
Pour a bit of the club soda into the shaker tin to grab the remaining egg cream; then gently pour atop the cocktail.
Garnish with freshly grated orange zest (optional)