Preheat the oven to 150C/300F/Gas 2. Butter the inside of a two-litre pudding basin.
Put the cream and chocolate in a medium non-stick saucepan and heat very gently, stirring regularly until the chocolate melts. Remove from the heat.
Place the egg yolks, Irish cream liqueur and sugar in a large bowl and whisk until pale.
Slowly pour the warm cream and chocolate mixture onto the eggs, stirring vigorously until thoroughly combined. Carefully pour the mixture into the buttered pudding dish and place in a large roasting tin.
Boil a kettle of water and carefully pour the just-boiled water into the roasting tin so it rises roughly 3cm/1¼in up the side of the dish. Take care that you don’t drip any water on the cream mixture.
Open the oven door, and using an oven-cloth to hold as the tin will be hot, place the pudding in the centre of the oven. Bake for 40-45 minutes. The custard is ready when it is almost set. If you move the dish, you should see the custard wobble like a jelly with a slight ripple under the surface. It will continue to firm up as it cools.
Take the roasting tin out of the oven, lift the pudding dish carefully from the water and set aside to cool for about an hour. Cover with cling film and chill in the fridge overnight.
Up to five hours before serving, make the caramel. Put the sugar and four tablespoons of cold water into a small saucepan and place over a medium heat for about a minute, stirring with a wooden spoon until the sugar dissolves.
Increase the heat a little and cook the sugar, without stirring, for 5-7 minutes, or until it turns golden-brown – the same colour as maple syrup. Uncover the custard and have close to hand ready for the caramel topping.
As soon as the caramel is ready, remove the pan from the heat. Do not touch or taste the caramel as it will be extremely hot. The caramel will continue to cook once it has been removed from the heat, so don’t allow it to become any darker before you take it off.
Brush a large metal serving spoon with oil and slowly pour the caramel over the spoon onto the cooled custard, ensuring it is covered as evenly as possible. Don’t pour into one area only or the hot caramel will begin to melt the cream. Tilt the dish to help it run to the edges if necessary. Leave to cool for 15 minutes before serving or keep covered in the fridge. (The caramel will begin to soften after a couple of hours.)
For the langues de chat biscuits, pre-heat the oven to 200C/400F/Gas 6 and line two baking trays with parchment paper.
Using an electric whisk, cream the butter and icing sugar together until light and fluffy. Beat in the vanilla extract, cinnamon and orange zest. Whisk in the egg whites one at a time and then fold in the flour.
Using a piping bag fitted with a plain 1cm/½in nozzle, pipe 6cm/2½in strips of the mixture onto the lined baking trays.
Bake for 6-8 minutes until the edges are slightly golden-brown. Leave to cool on the tray.
Serve the caramel-topped Trinity cream with the langue de chat biscuits alongside.