For the custard, whisk 150g sugar, the egg yolks and cornflour in a bowl until pale and smooth. Pour 300ml cream, the milk and 65ml of the alcohol into a saucepan. Split the vanilla pod, scrape out the seeds and add to the cream with the pod. Heat until steaming but not boiling, then pour the hot liquid onto the yolks, whisking as you go. Strain the liquid through a sieve into a clean saucepan and discard the vanilla pod. Return to a low-medium heat and whisk for about 10 mins until very thick. If you get lumps, simply whisk them out. Pour the custard into a jug and cover with cling film directly on the surface. Chill for 11 /2 hrs.
Arrange half the profiteroles in the base of a 2-litre trifle bowl. Spoon 2 tbsp of the remaining alcohol over the profiteroles along with the orange juice, then crumble over the biscuits. Trickle the custard over the profiterole base. Arrange the remaining profiteroles on top of the custard, working around the edges first, then filling the centre. Arrange the clementine slices around the edge of the bowl, tucking them around the profiteroles
Whisk the remaining alcohol, 500ml cream, 50g sugar and the orange zest until holding soft peaks. Spread the mixture over the profiteroles, right to the edge of the bowl, then return to the fridge until you’re ready to serve. Can be made a day ahead up to this point.
For the meringue, put the egg whites, the remaining 175g sugar, 1 tbsp water and a good pinch of salt in a heatproof bowl over a pan of simmering water, making sure the bowl doesn’t touch the water. Whisk until thick and leaving a prominent trail from the beaters – this will take about 4 mins. Take the bowl off the heat and continue whisking for another 3 mins until cooled slightly and very stiff.
Spoon the meringue onto the trifle, creating peaks and troughs with the back of a spoon. Use a blowtorch to scorch the meringue if you have one (but don’t hold it too close to the bowl if it’s made of delicate glass!). Best served straight away, but will keep for a day in the fridge.