Help my ice-cream won't thicken: Salted Butter Caramel Icecream

Have I mentioned that I love making ice-cream? Ever since picking up an ice-cream maker for $8 at an op shop 2 years ago, I haven't needed much of an excuse to try out a new flavour. Pistachio Praline is a favorite, the tiramisu flavour I created is always a hit, and eggnog icecream goes beautifully with plum pudding at Christmas.

My latest flavour attempt is related to my other new favourite thing to make- caramel. I found a great sounding recipe for Salted Butter Caramel Icecream on guru David Liebovitz's delicious blog. I brought the sugar to a dark amber colour, then added a 1/2 tsp of Murray river salt, salted butter, cream and a cup of milk. 5 egg yolks were incorporated and the mix returned to the heat to thicken to a creamy, luscious brown custard. Adding the custard to a 2nd cup of milk, I popped it into the fridge overnight to chill and then churned it in my icecream maker until the custard thickens into...thickens into....thickens... into.... Wait, I've made icecream many times before, I don't tolerate failure, thicken damn you!

After an hour of churning my custard remained just that, a custard. Deciding I hadn't chilled the bowl enough, I took it over to daughter Hayley's flat where my icecream sandwiched between Dutch stroopwaffels was to be the dessert to a Mexican dinner (mmm pulled chicken on homemade tortillas). Their icecream churn bowl is left in the freezer in case they get the sudden urge to make icecream, so she'll churn it for me. An hour later I get an SMS - "Houston we have a problem...." The custard is still, stubbornly, custard. As a stop-gap measure we put the custard in the freezer and had a semi-frozen dessert - delicious flavours but not ice-cream.

Determined to try again I trolled the internet, checking out messageboards for "Help my icecream won't thicken" for a clue. Everything I read talked about whether the custard was left overnight ( it was) whether the bowl was completely frozen solid (ditto) whether the amount of custard was too much for the churn (no, exactly what was specified), whether the custard was thick enough (yes), only egg yolks used (yup), and found little to enlighten me. So I went back over the steps in my mind and suddenly it hit me: Low-fat milk! We always use low-fat milk and although I had added extra cream as I usually do to compensate, the milk I had accidentally bought was actually no-fat Physical. D'oh.

On Sunday night then I made a whole new batch of custard, using full-cream milk, following every step religiously, chilling both custard and bowl for 24 hours and then on Monday put it to the test. My custard began to do its thing, but at the end of the churning it was still softer than usual. A couple of hours in the freezer produced a lovely final product though:

Having revisited my high school physics I now suspect that the extra salt, while small, probably also had an effect on the final product.

David Leibovitz doesn't mention any problems with the salt and possibly it is the case that my small domestic icecream churn doesn;t have temperatures low enough to counteract what salt there is.

So now I have an excuse to make another batch, except this time without the salt.