In a food processor or blender, pulse the whole Oreos into fine crumbs. (Alternatively, put the cookies into a freezer bag and crush them using a rolling pin).
Transfer ground crumbs to a medium bowl, add melted vegan butter and stir until crumbs are evenly moistened.
Press the mixture onto the bottom and up the sides of a 9 or 9,5-inch (23/24cm) tart pan with removable bottom (or pie pan). Place in the fridge or freezer for 15 minutes to firm up (or bake it for a crispier result *see notes).