Prepare the biscuit base: Place the digestive biscuits in a sealed plastic bag and crush them with a rolling pin until you have fine crumbs with a few slightly larger pieces for texture. Alternatively, pulse them in a food processor until they resemble wet sand. Transfer the crumbs to a mixing bowl, pour in the melted butter and golden caster sugar, and stir until every crumb is coated. The mixture should clump together when pressed between your fingers.

Form the crust: Tip the buttery crumbs into a 23cm loose-bottomed tart tin. Press them firmly and evenly into the base and up the sides using the back of a spoon or the bottom of a glass. Pay attention to the edges — a compact crust holds together better after chilling. Place the tin in the refrigerator for 20 minutes to set. The surface should feel firm and cool to the touch.

Make the chocolate ganache: Pour the double cream into a small saucepan and warm it over a medium heat. As soon as you see tiny bubbles forming around the edge — do not let it boil — remove the pan from the heat. Add the dark chocolate, milk chocolate, cubed butter, vanilla extract, and sea salt. Let it sit undisturbed for 2 minutes, then stir gently with a spatula until the mixture is completely smooth and glossy. You should see a deep, mirror-like sheen across the surface.

Cool the ganache slightly: Set the ganache aside at room temperature for 15 minutes. It needs to cool enough that it won't melt the cream cheese later, but it should still be pourable. Stir it occasionally; it will thicken subtly and lose its initial heat.

Prepare the cream cheese layer: In a large mixing bowl, beat the cream cheese with an electric mixer until it is soft and fluffy, about 2 minutes. Sift in the icing sugar and beat again until fully incorporated. The mixture should be smooth, pale, and free of any lumps.

Combine the layers: With the mixer running on low speed, slowly pour the cooled ganache into the cream cheese mixture. Stop to scrape down the sides of the bowl, then beat on medium speed for 30 seconds until the filling is uniformly dark, thick, and velvety. It should hold a soft peak when you lift the beaters.

Assemble the pie: Remove the chilled crust from the refrigerator. Spoon the chocolate filling into the crust and spread it evenly with a spatula, smoothing the top. Give the tin a gentle tap on the worktop to release any air bubbles. The surface should be flat and glossy.

Chill and serve: Place the pie in the refrigerator for at least 4 hours, preferably overnight. The filling should be firm to the touch and slice cleanly. Before serving, dust the top with a light layer of cocoa powder if desired. My kids absolutely devour this every time I make it, and the slices come out perfectly neat when the pie is well chilled.