How long should the potatoes be simmered before putting into the baking tin? Also, the quantities used mean the liquid doesn't cover all the potatoes in the saucepan. Is this right or should they be covered in order to par-cook? Finally a tablespoon of salt seems like an awful lot - is that correct?! Trying this for the first time, so advice would be much appreciated.
Nigella's Creamy Potato Gratin (from Nigella Bites and on the Nigella website) cooks the potatoes in a saucepan with the cream and milk. The cooked potatoes are then transferred to a baking dish and finished in the oven. The simmering time will depend slightly on the size of the pan, the thickness of the potato slices and how briskly they simmer for. So we would suggest simmering the potatoes for 15 minutes and then checking them every 5 minutes to see if they are cooked. The potatoes should be tender but not breaking up or mushy.
There should be just enough liquid to come to the top of the potatoes in the saucepan. You may need to gently push the potatoes down in the saucepan as they come up to a simmer and they will tend to sink down into the liquid as they cook. If it looks as if there is really not enough liquid then add a little extra milk. The 1 tablespoon of salt is for sea salt flakes and these do not pack very firmly into a spoon measure. So 1 tablespoon of salt flakes equates to around 1 1/2 teaspoons of free-flowing table salt, but please feel free to use a quantity of salt to suit your own taste.