To make the crème mousseline, bring the milk and vanilla pod just to the boil in a wide saucepan. Remove from the heat and leave to infuse for 10 minutes. Meanwhile, whisk together the eggs, egg yolks, sugar, kirsch and cornflour in a bowl just until smooth and creamy. Remove the vanilla pod from the milk, then pour through a sieve onto the egg mixture, whisking well. Pour the mixture into the washed saucepan, set over medium heat and stir constantly until the mixture boils and thickens; this will take about 4 minutes. It’s important to keep stirring to avoid the custard going lumpy.