Soak the gelatin sheet in cold water for 5 minutes until fully softened. Squeeze out excess water and set aside.

Melt 70g butter over a double boiler and let it cool slightly until warm.

Add the Biscoff cookies to a large bowl and crush them using a smasher until very fine (large crumbs may cause the crust to crack).

Add the melted butter and stir with a silicone spatula until all crumbs are evenly coated.

Transfer the mixture into an 8-inch tart pan and press firmly using the bottom of a glass to compact both the bottom and sides.

Refrigerate for 30 minutes to set.

Add the dark chocolate pieces and heavy cream to a small pot or heatproof bowl. Melt over a double boiler, stirring constantly until completely smooth.

Add the butter and stir until silky and lump-free.

Pour the chocolate filling into the chilled cookie crust and gently tap to release air bubbles.

Refrigerate for 2 hours until fully set.

In a bowl, mix the sugar and cocoa powder. Add the hot milk and whisk until everything dissolves completely and the mixture is smooth.

Add the softened gelatin sheet and stir quickly until fully dissolved.

Strain the glaze through a fine sieve to remove any lumps or bubbles — this step ensures the mirror-smooth finish.

Pour the glaze gently over the fully set chocolate filling, tilting the pan slightly to help the glaze spread evenly.

Refrigerate for another 30 minutes until the glaze is set.

Decorate with chocolate pearls if desired.

Warm the sides of the tart pan using a hairdryer for 30 seconds or wrap with a warm towel to slightly loosen the edges.

Remove the ring and base, transfer the tart to a serving plate, slice, and enjoy.