On 'Vinaigrette' - the most useful sauce .......

Vinaigrette is rather like roast potatoes or chicken soup - everyone uses the same basic ingredients, and everyone's vinaigrette still tastes unique! The only ready-made one I might buy is the Carrefour Vinaigrette Nature - which I can only get in Fracne unfortunately. -

I usually make up a quantity which I keep in a screw-top jar in the fridge, and sometimes just add to it as it decreases. 

1. For basic Vinaigrette I use :  
1 part cider vinegar or wine vinegar or Honeygar (which is slightly sweet) - to
4 to 6 parts of olive oil - (I like my vinaigrette more oily than sharp) 
- you have to taste it as you go. 
1 tsp to 1 tablespoon - (to your own taste) - of grainy or plain Maille Dijon mustard
S&P, 
clove of crushed garlic and 
a little sugar - lid on jar and shake well. Keeps really well for ages in the fridge.

There are so many additions too - dried herbs, fresh herbs, lemon juice instead of vinegar is also really nice .... different oils, etc. I sometimes add some Flaxseed Oil along with the Olive or Sunflower Oil, as I like the nutty flavour.

Elizabeth David suggested having ready 2 soft-boiled eggs, scoop out the yolks and add them to the sauce - (this sounds rather nice, though haven't tried it) - this sauce should be made an hour or so before it's eaten. This versatile sauce can be used with fish, vegetables, chicken, salad .......

2. Fruity Vinaigrette (c/o Ottolenghi)
1 tablespoon of preferably fresh Orange Juice - use remaining juice from above oranges plus some extra
1 tablespoon of Honeygar - (cider vinegar and honey ready-mixed)
3 tablespoons Sunflower Oil
Salt and Black Pepper