2 - Use a mandolin to slice your potato - so you get even thin slices without cutting your thumb while slicing with a knife.
3 - Use the guard for the mandolin as you want to slice the potato, not your fingers. I have seen some very nasty accidents with people using madolins - the worse thing is when you get complacent, start thinking of the next thing you have to do, or someone calls you while you're slicing, you look round, and suddenly you're on your way to casualty.
In one particular incident at Claridges we sent one chef off to sit down when he felt a little faint after a nasty mandolin cut, blood dripping through the gauze he held to his finger. When the first aider took a look it, the end of the finger was missing. After careful inspection by his co-worker it was found next to the pile of cucumber he had been cutting on the mandolin. Luckily they were able to sew it back on at casualty.
The moral? use the guard, and keep paying attention.
4 - Before you start slicing the potato you have put your double cream on simmer to reduce. By the time you have finished slicing it should have reduced by more than half - like the concistency of sticky toffee sauce (but not the colour obviously). Now mix the potatoes in thoroughly and allow to cook on low heat for 10 minutes turning frequently. This produces firmer dauphinoise which you can cut out with a cutter. Also the more cooking you do on the stove first the less time they take in the oven.
If you want softer dauphinoise you just add more cream.
5 - Mix in some cheese and allow to melt. You could also mix in grain mustard, chorizo, dried onions or a number of other items for different flavours, though I prefer to keep it plain.
At Claridges we would used gruyere cheese for dauphinoise, but in the Cotswolds I like to use St. Kennelm from the nearby award winning Gorsehill Abbey Farm.
Once the cheese has melted transfer the dauphinoise to a baking tin and smooth off the top. You can sprinkle with more cheese. Now place in a deeper tray and fill with hot water 2/3 way up the side of the dauphinoise tray and cover the top with foil. Bake in the oven for c. 45 - 60 minutes till soft. Then remove foil for a further 5 minutes and allow the top to gratinate. Cooking it in a bain marie like this saves the edges from burning. Covering the top with foil means it cooks through rather than burning the outside and leaving the middle raw.
5.5 - I now add garlic as well. Amounts? 5 - 6 baking potatoes (estima) yesterday with c. 400ml double cream reduced, 1 clove garlic made a 9 inch square, 1 1/2 inch deep tray which does c. 10 portions, unless everyone really likes it and want seconds ;-)
Why have my dauphinoise gone black on the top?
Oxidisation. Potaotes naturally go brown then black once they are exposed to the air. This is countracted by either putting them in water or cooking them. If the potatoes are going grey on top of the dauphinoise it means they're not being cooked fast enough - oven temperature is too low, or you put them in to a cold oven. If you cook the potatoes first (as described in 4, above) this shouldn't happen.
This can also happen at certain times of the year (crossover between the seasons), and also if the potatoes have been dug after prolonged periods of rain. You should also keep potatoes out of the light - either sunlight or electric light.
Despite their appearance however, they are fine to eat.
Can I freeze dauphioise potato?
Yes you can. Once cooked, leave it it cool. Once cool you could either cut it out into portions (either square ones with a knife, or round/ oval with a pastry cutter) and freeze them, covered, on a flat tray. Or you could just freeze it whole in the tin/ dish you cooked it in. You can either leave it to defrost in the fridge overnight or re-heat from frozen.
Re-heat in the oven or microwave - though it is best in the oven because it crisps up on the top. From defrosted/ chilled, the cut-out individual portions just need 3 minutes in the microwave (750 watts) on a plate and covered with cling film. About 15 - 20 minutes in the oven at 180 oC. If re-heating from frozen increase the cooking time.
You are best leaving a large frozen tray to defrost overnight. If not though, if using the oven cover with foil to begin with so the top doesn't burn before the middle is near luke warm, remove foil for the last 15 minutes.
Instead of using a large tray as above you can spoon them into individual ramekins - one ramekin per portion, cover with foil and cook for around 45 minutes. Remove foil for 5 minutes to brown the top if neccessary. These can be made the day before, chilled, fridged and re-heated as you serve your starter.