Start by making the custard: in a pan, bring the milk and double cream to a boil, then remove from the heat.
In a large pan, whisk the eggs, sugar and cornflour until foamy, then very slowly pour the hot milk and continue whisking. Bring back on the lowest heat and stir continuously until you reach the desired consistency (about 10 minutes). Then reserve, cover and refrigerate for a couple of hours.
In a mixing bowl, whisk the double cream with the icing sugar until you have a nice and smooth chantilly consistency.
Then add a layer of custard, then whipped cream, then cherry jam, then repeat with another layer of ladyfingers, custard, and whipped cream. You can vary the order if you prefer.
Decorate with a few extra glacé cherries on top and refrigerate until pudding time!