Crush the cocoa biscuits into fine crumbs (a food processor works well, or crush by hand in a sealed bag). Mix thoroughly with the melted butter until the texture resembles wet sand. Press firmly into the base of a lined springform pan, packing it down evenly with the back of a spoon. Chill in the fridge for at least 20 minutes while you prepare the next layer.

In a bowl, combine the hazelnut praliné and hazelnut paste until smooth. Fold in the crushed crêpes dentelles and a touch of vanilla until evenly coated, the mixture should be crumbly but hold together when pressed. Spread this layer evenly over the chilled crust, pressing down gently. Return to the fridge to firm up while you make the filling.

In a large bowl, beat the cream cheese and mascarpone together until smooth and lump-free. Add the powdered sugar and vanilla, and mix until combined. In a separate bowl, whip the heavy cream to soft-medium peaks. Gently fold the whipped cream into the cream cheese mixture in batches, being careful not to deflate it this keeps the filling light and mousse-like.

Pour the filling over the praliné crunch layer, smoothing the top with an offset spatula or the back of a spoon. Tap the pan gently on the counter to release any air bubbles. Cover and refrigerate for at least 6 hours, or overnight for the best texture and the cleanest slices.

Gently heat the cream until just simmering, then pour over the white chocolate in a heatproof bowl. Let sit for a minute, then stir until smooth and glossy. Stir in a touch of vanilla. Let the ganache cool slightly until it thickens just enough to hold on top of the cheesecake without running off the edges.

Once the cheesecake is fully set, carefully release it from the springform pan. Pour the ganache over the top, letting it spread naturally toward the edges (or gently push it with a spatula for an even finish). Return to the fridge for 10-15 minutes to let the ganache set slightly before slicing. Serve chilled, and use a sharp knife wiped clean between slices for the cleanest cuts.