Line the base of a 23 cm/9-inch springform tin with baking parchment. Crush the digestive biscuits into fine, even crumbs, then stir them through the melted butter until every crumb is coated.

Tip the biscuit mixture into the prepared tin and press it firmly across the base, paying particular attention to the edges. Use the flat bottom of a glass or measuring cup to compact the crust, then refrigerate it while making the filling.

Beat the softened cream cheese, sifted icing sugar, Baileys, and optional vanilla extract until smooth and creamy. Stop mixing as soon as the ingredients are combined to avoid overbeating the mixture.

In a separate bowl, whip the cold double cream to soft-to-medium peaks. The cream should hold its shape but still look smooth rather than grainy or stiff.

Gently fold the whipped cream into the Baileys cream-cheese mixture in batches. Use a large spatula and fold slowly until no pale streaks remain, keeping as much air in the mixture as possible.

Spoon the finished filling over the chilled biscuit base and spread it into an even layer. Smooth the surface with a palette knife or the back of a spoon.

Cover the tin and refrigerate the cheesecake for at least 6 hours. Overnight chilling is preferable because it allows the filling to firm completely and makes slicing much easier.

For the decoration, whip 150 ml double cream with 1 tablespoon icing sugar and 1–2 tablespoons Baileys until suitable for piping or spooning. Add swirls of cream to the chilled cheesecake, then scatter over grated chocolate, chocolate curls, or a light dusting of cocoa powder.

Run a thin knife warmed under hot water around the edge of the cheesecake before releasing the springform tin. Wipe the knife between cuts and serve the cheesecake cold for the firmest texture.