Heat the lactose free milk and vanilla pod in a pan until nearly boiling, then leave to infuse for 10-15 mins. Whisk together the egg yolks with 2 tbsp sugar until pale and light, then whisk in the corn flour to make a smooth paste.
Whisk the warm milk into the paste. Pour the mixture into a pan, then cook for 3-5 mins until thickened and the mixture coats the back of a wooden spoon. Pour through a sieve into a large bowl, discarding the vanilla pod, then leave to cool a little.
Whisk the egg whites until trebled in size and stiff peaks form. Add the remaining sugar, a little at a time, whisking well between each addition, until the mixture is thick and glossy.
Stir the lemon juice or eau de vie into the custard mix. Add a third of the meringue to the custard, stir well to incorporate, then carefully stir through the remaining meringue in two goes.
Scatter the fruit into a large, shallow heatproof dish. Put under a medium grill for 3-5 mins to soften slightly. Spoon over the custard mix. Return to the grill for 3 mins until the topping is golden brown.