Lay half the biscuits in a rectangular deep dish (mine measured28cm x 21cm), pour the warm custard over them and then lay out the rest of the biscuits on top. Allow the dessert to cool down, cover it with baking paper and then cling wrap to avoid any moisture from dripping on the biscuits. Place the baking dish in the fridge so the custard can set and chill for at least 4 hours or overnight.
I've also used lactose free milk when making this recipe and it worked just as well. And to make it completely lactose free there are some plain biscuits available at the supermarkets that would be suitable to use instead.