This recipe is an adaptation of a basic milk punch from the New York restaurant Betony, known for their choose-your-own-adventure option for milk punch. And you can make it up to a week ahead of time! It's not like those cream-heavy versions you might see akin to eggnog—the milk ends up acting more like an egg white in a flip here, but on a punch-size scale, or you can drink the base on its own once the curds have settled to the bottom. I made the rosemary simple syrup with Simply Organic's dried rosemary which turned out lovely and big on flavor. —Samantha Weiss Hills
Make the rosemary simple syrup: In a small saucepan over medium-low heat, mix the water, sugar, and dried rosemary together. Heat and stir just until the sugar is dissolved, then remove from the heat. Let sit for 20 minutes before straining into a jar. Let cool completely before using.
Make the milk punch: Combine cooled tea, lemon juice, grapefruit juice, rosemary simple syrup, and gin in a large pitcher or very large bowl.
In a medium sauce pan over medium heat, bring the milk to a bare simmer. Immediately pour the milk into the gin mixture. (The milk will curdle right away). Cover and chill at least 1 hour and up to 24 hours.
Strain the mixture through a fine-mesh sieve lined with cheesecloth into a large bowl. Cover and chill until cold. (Any remaining curds should settle at the bottom of the bowl).
Carefully ladle the clarified punch into a clean pitcher, leaving any remaining curds behind. Chill until ready to serve. (This punch base can be made 1 week ahead.)
Make the cocktails: For each cocktail, combine 1 1/2 ounces gin and 2 ounces milk punch base in a cocktail shaker and fill shaker with ice. Shake for about 30 seconds, and strain into a rocks glass with one large ice cube.