To make a good Dauphinoise, you need a) not to be on a diet b) not to have made any after supper plans beyond falling asleep under the FT c) with a good Waitrose or farm shop nearby.
There are few ingredients, but they must be the best.
A pound of lovely King Edward or Desiree potatoes;
A small pot of Jersey cream;
half a pint of buttercup yellow milk;
A slice of onion;
A crushed clove of garlic;
Half a tablespoon of chicken demi-glace*;
2oz reserve Gruyere grated so finely it resembles a cloud;
Salt and pepper.
Mix together your milk and cream and steep the slice of onion in it for an hour at room temperature. Then pour into a saucepan, heat through with the crushed garlic, bayleaf, nutmeg, demi-glace, salt and pepper but do not allow to boil - take it off the heat when curling wisps of steam begin to rise from the surface and discard the bayleaf and onion.
Meanwhile, peel and wash your potatoes; then slice them very finely so that they are transparent and rinse again to get rid of the starch. Layer in a casserole. Pour over the milk and cream mixture, top with the Gruyere and bake at gas mark 2 for an hour and a half.
Serve with duck, slow roasted beef, left over chicken.
*Demi-glace: a thick chicken stock. After making your initial stock (carcass, halved large onion, roughly sliced carrots, halved turnip (optional), 2 stalks celery, half a lemon, 12 peppercorns, bouquet garni, bayleaf, enough water to cover; bring to boil, skim off froth as it forms, reduce by half, top up with water and repeat process until no no scum is left; pour through a funnel into a clean bowl, allow to cool, refrigerate overnight) carefully remove the layer of fat that has formed on the top of your now jellified, chilled stock, place in a saucepan and reduce by half (demi-glace). Refrigerate overnight, remove any remaining fat, heat and reduce by half to form a glace. SO much better than chicken stock cubes even if it does take 2-3 days; can be frozen in icecube trays and used when necessary.