Make simple syrup by stirring together 1/4 cup sugar and 1/4 cup boiling water. Cool in the fridge.
In a cocktail shaker without ice, combine the rum, lime juice, simple syrup, egg white (if using) and heavy cream. Shake vigorously until well blended. Pour the mixture into a blender with 1/4 cup of frozen pineapple chunks and a handful of regular ice cubes. Blend well.
Pour the mixture into a martini or highball glass. Leave room to top the drink off with a healthy splash of ginger beer. Taste. Want more ginger beer? Add some. Garnish with a chunk of pineapple or wedge of lime.
Recipe Notes
For simple syrup: (stir together 1/4 cup sugar with 1/4 cup boiling water & cool.)