Old Fashioned
Lemon zest strip should be about 3" long. Add lemon zest and citrus syrup to a large bowl and muddle until fragrant, about 30 seconds. Stir in rum, boiling water, brandy, beer, and lemon juice, then gently stir in milk until curds form. Cover and refrigerate until flavors meld, at least 2 hours or up to 1 day. Line fine mesh strainer with a double layer of coffee filters and set over serving pitcher or large container. Working in batches, gently pour rum-milk mixture into prepared strainer and let drain completely. Discard solids. Cover punch and refrigerate until well chilled, about 1 hour. Serve in chilled glass of your choice.