Step 1

In a saucepan, bring heavy cream, granulated sugar, finely grated lime zest, and a pinch of kosher salt to a boil over medium heat. Cook, stirring often, until reduced to 2 cups, 8 to 10 minutes.

Step 2

Remove from heat; stir in fresh lime juice. Let cool 20 minutes, then strain through a fine mesh sieve into a liquid-measuring cup; discard solids. Divide evenly among 6 glasses. Refrigerate until set, about 2 hours. Top cups with lightly sweetened whipped cream, crumbled graham crackers, and more finely grated lime zest; serve.