Combine the orange liqueur, white rum, lemon juice and simple syrup in a cocktail shaker filled with ice. Shake for 30 seconds. Strain into a rocks glass or large coupe.
Float the lemon shell in the glass and fill with the 151-proof rum. Using a long match or lighter, very carefully ignite the rum. To extinguish the flame, use a spoon or stirrer to press the lemon into the cocktail.