Start by pulsing the biscuits and toasted hazelnuts in a food processor until they form a fine crumb. Mix the melted butter and a pinch of salt into the crumbs until fully combined. Press the mixture firmly into the base and sides of a tart pan, then refrigerate for 30 minutes to set.
Chop your chocolate into small pieces for even melting. Heat the heavy cream until warm but not boiling, then pour over chocolate and hazelnut paste. Stir gently until smooth and glossy, forming a luxurious ganache.
Pour the ganache over the chilled crust, spreading evenly. Smooth the top with a spatula and refrigerate for at least 1 hour until fully set. For an extra touch, sprinkle chopped hazelnuts or cocoa powder on top before serving.