Ok, so this isn't really gonna help the BLWers, but it's fab for when they've gone to bed!
4 egg yolks
250ml milk
500ml double cream
100g caster sugar
2 heaped tablespoons horlicks or ovaltine
A couple of packets of maltesers, roughly crushed
Beat the egg yolks, milk, sugar and horlicks together in a saucepan and heat gently whilst continuously stirring. Keep going until it starts to thicken. This was described to me as when if forms a glossy sheen on the back of a wooden spoon. I think it took about 6 or 7 minutes. You absolutely mustn't let it boil.
Pour the double cream into a bowl or jug and then add the egg mixture and stir. Put it in the fridge. Once chilled, transfer it to tupperware and put it in the freezer.
Now, the recipe I used said get it out every 20 minutes and whisk it to get rid of the ice crystals, and at the point when it is soft add the maltesers. I made this late at night though, and after I had got it out a couple of times it was still runny and I wanted to go to bed. So I just dumped the maltesers in and stirred it and left it. Worked perfectly!