Muddle 8 large mint leaves in a cocktail shaker. Add 1 egg white, 2 ounces gold rum, 1 ounce thawed frozen orange juice concentrate and 1/2 ounce each lime juice, simple syrup and heavy cream; shake 30 seconds. Add ice and shake 30 more seconds. Strain into a glass and top with seltzer. Garnish with an orange slice.