Add all ingredients into a shaker with ice and shake until well-chilled.
Strain into a double Old Fashioned glass over fresh ice.
Garnish with half of a grapefruit wheel.
*Tarragon simple syrup: Combine 1 cup white sugar and 1 cup water in a small saucepan. Bring to a boil, reduce heat and simmer until sugar is dissolved. Remove from the heat and add 1/4 cup fresh tarragon sprigs. Steep for 15 minutes or until desired flavor is achieved, then strain out solids.