Finely crush the Oreos with a food processor or blender. Stir crumbs together with 8 tablespoons melted butter until well combined. Press into the bottom and sides of a pie pan. Freeze the crust for 10 minutes until set
Combine the remaining 8 tablespoons of butter and brown sugar in a small saucepan. Cook over medium heat, whisking constantly until mixture begins to bubble. Continue cooking, whisking constantly, for 1 minute. Remove from heat. Slowly whisk in 1/4 cup heavy whipping cream until smooth. Cool caramel for about 15 minutes.
Pour the caramel over the Oreo crust, then return to the freezer for about 30-45 minutes until just chilled and set.
Chop the dark chocolate bar into fine pieces.
Place chopped chocolate in a glass bowl. In a saucepan, bring 1 cup heavy whipping cream to a simmer over medium-high heat. Pour the cream over the chocolate chips and let sit for 5 minutes, then whisk until completely smooth.
Pour the chocolate over the caramel and freeze for a final 30 minutes, until just chilled and set. OR refrigerate, covered, until ready to serve. Before serving, sprinkle the top with any flaky sea salt like kosher salt.