Step 1

Preheat oven to 350°F. Blend cookies in a food processor until finely ground (you should have about 1 1/2 cups). Add sugar and butter; pulse until crumbs are evenly moistened. Press evenly into bottom and up sides of a 9-inch round fluted tart pan with a removable bottom. Refrigerate 15 minutes. Bake until fragrant and slightly darker brown, about 10 minutes. Let cool completely.

Step 2

Meanwhile, in a small saucepan, whisk together egg, yolk, and condensed milk, then whisk in lime juice. Place over medium-high heat and bring to a simmer. Cook, whisking constantly, 1 minute. Remove from heat and whisk in chocolate until melted. Transfer to a large bowl; let cool completely.

Step 3

Whisk cream to soft peaks. Whisk thoroughly into cooled lime mixture until smooth. (It may look slightly curdled at first, but keep whisking!) Spoon into a swoopy layer in crust. Refrigerate until set, at least 2 hours or, lightly covered, up to 12 hours. Serve, sprinkled with lime zest.