Sift together the flour, salt, and baking soda.
In a standing 5-quart mixer with the paddle attachment, cream the butter, sugar, and zest. Paddle on medium-high speed until light and fluffy, about 5 minutes.
Add the eggs, gin, and grapefruit juice and paddle until incorporated. Scrape down the sides of the bowl with a rubber spatula. Pour in the flour mixture while mixing on low speed and mix until the dough comes together.
Cover the dough and let rest in the refrigerator for 5 hours or overnight. When ready to bake, preheat the oven to 350°F/177°C. Scoop tablespoon-size cookies onto a sheet tray lined with parchment paper or a Silpat. Bake until done, 10 to 12 minutes. Remove from the oven and allow to cool.