Place an ice cube into a rocks glass
Pour 0.15 oz of sugar syrup, 0.35 oz of Oloroso sherry, 1 oz of dark rum and 1 oz of overproof rum into a mixing glass
Add 1 dash of Angostura bitters and 2 dashes of orange bitters
Fill the glass with ice cubes and stir gently
Strain into the rocks glass
Garnish with orange and lemon zests