Put the milk and half the sugar in a saucepan over medium heat and bring to the boil, stirring occasionally.
Split the vanilla bean lengthways and add to the milk - or add vanilla essence.
In a bowl (not plastic), whisk the egg yolks with the remaining sugar. When the sugar has dissolved, stir in the cornflour.
When the milk has boiled, pour it in to the egg yolk and sugar mixture. Stir well and then pour the mixture back into the saucepan. Place over a low heat, stirring constantly and allow the mixture to thicken.
Strain the mixture into a mixing bowl. Remove the vanilla bean and scape the seeds into the mixture.
Cover with plastic and allow to cool. When cool, pour in cream and pour the mixture into an ice cream maker, or put into a large bowl and place in the freezer, stirring every so often until set.
Melt the chocolate in bowl over hot water bath (bain marie).
Stir in butter and allow to melt.
Stir in orange liqueur and cream and continue to stir until it has become a smooth, rich sauce.
Handy Hint: If using vanilla bean there will be tiny black dots in the finished product, this is perfectly normal (in fact it shows the ice cream is genuine!).
Leftover Potential: Keeps well in the freezer for several days.
Per serving: 358 Calories (kcal); 30g Total Fat; (72% calories from fat); 5g Protein; 22g Carbohydrate; 191mg Cholesterol; 27mg Sodium Food Exchanges: 0 Grain(Starch); 0 Lean Meat; 0 Vegetable; 0 Fruit; 6 Fat; 1 1/2 Other Carbohydrates