To give a luxurious silky texture to cocktails, this simple syrup (a syrup made by dissolving sugar in water) is thickened slightly with xanthan gum.
Fill a rocks glass with ice. In a cocktail shaker, stir together the Cognac, rum, simple syrup and both bitters. Pour into the rocks glass and garnish with the orange twist.
Demerara rum is a type of dark rum made in Guyana.