Preheat the oven to 350 degrees F. Crush the Oreo cookies in a food processor until they form fine crumbs. Mix the crumbs with the melted butter until evenly coated.

Press the mixture firmly into the bottom and sides of a 7-inch tart pan. Bake for 8 minutes, then let the crust cool completely on a wire rack.

Place the chopped dark chocolate in a heatproof bowl. Heat the heavy cream in a small saucepan over medium heat until it just starts to simmer.

Pour the hot cream over the chocolate. Add the black cocoa powder, vanilla extract, and salt. Let it sit for 1 minute, then stir until smooth and fully combined.

Pour the chocolate filling into the cooled crust. Smooth the top with a spatula. Refrigerate for at least 2 hours until set.