Ramona Rum Fizz

In a cocktail shaker, combine rum, juices, simple syrup, bitters, and egg white; dry shake. Add heavy cream and ice and shake vigorously. Into a Collins glass filled with ice and 2 ounces soda water, strain cocktail, filling the glass. Tap bottom of glass for 15 to 20 seconds to get bubbles to settle. Add remaining soda water to shaker with the remainder of the cocktail. Double strain into glass, lifting the head of the fizz above the rim of the glass. Garnish with grapefruit twist and metal spoon straw.