Make crust: Preheat oven to 350ºF. Break cookies into a food processor. Pulse until finely ground. Add butter, sugar and salt; pulse to combine. Use your fingers to press mixture into a 9-inch tart pan with a removable bottom. Set tart pan on a baking sheet. Bake until crust is dry and crisp, about 10 minutes. Transfer to a wire rack to cool completely.
Make filling: Place chocolate, butter and salt in a medium bowl. Warm cream in a small pot over medium-high heat until steaming, about 3 minutes. Pour cream over chocolate mixture, let stand for 2 minutes, then whisk until smooth. Add vanilla, bourbon and zest, if desired; stir until well combined. Pour chocolate mixture into crust. Refrigerate until well chilled and set, about 4 hours. Slice and serve.
