Add all ingredients into a shaker with ice and shake.
Fine-strain into a cocktail glass.
Express the oil from a grapefruit twist and drop in to garnish (or garnish with a grapefruit wedge).
*Honey syrup: Add 1/2 cup honey and 1/2 cup water to a small saucepan over medium heat. (You can experiment and decide how much of a honey flavor you want in your syrup. The more honey you use, the thicker the syrup and stronger in flavor it will be.) Stir until blended. Strain into a jar and seal tightly with a lid. Will keep for 1 month in the refrigerator.