Crush Biscoff cookies into fine crumbs using a food processor or zip-top bag and rolling pin. In a mixing bowl, combine with melted butter and cookie butter until thoroughly blended.

Transfer the crumb mixture into a tart pan, pressing it firmly to form an even layer.

Heat heavy cream over medium heat until it simmers, then pour over chopped chocolate and let sit for 5 minutes. Stir until smooth.

Pour ganache into the cooled crust and spread evenly.

Cover the tart with plastic wrap and refrigerate for at least 4 hours or overnight.