Add all the ingredients into a shaker with ice and shake.
Strain into a chilled coupe.
Garnish with grapefruit zest.
*Fennel cordial: In a saucepan, bring 10 oz water and .25 gram dried loose fennel seeds to a boil, and simmer for 10 minutes. Add .7 lbs fine sugar, and stir until dissolved. Fine-strain into bottles.