Salad dressing

This is sometimes called a French dressing.

Ingredients
oil
vinegar
salt, pepper, mustard

Equipment
small jar with lid

time:
mixing ingredients

Preparation process

You can buy a salad dressing if you prefer, if you make your own, you can get the flavour that you want. The minimum ingredients are and . I would suggest olive oil and balsamic vinegar, but if you want to use ordinary vegetable oil and malt vinegar, then why not!
The proportions of oil and vinegar are up to you. Use less vinegar than oil. I have heard of proportions from twice as much oil as vinegar to twelve times as much! Some vinegars are stronger than others, some have a more pleasant taste than others, and some people like the taste of vinegar more than others. I recommend starting with a proportion 2:1 (oil: vinegar) and then experiment. Try altering the types of oil and vinegar as well.
Salt and pepper add flavour. Oil and vinegar don't naturally mix, and tend to separate. Mustard helps them to mix, and helps the flavour as well, of course. You need small amounts of all these.
An easy way to make the dressing is to put the ingredients in a small bottle or jar with a lid, put the lid on, then shake it hard.
Don't use too much dressing on a salad! If you have a strong tasting dressing, then you will need even less.
As for additional ingredients, Ogden Nash has some strong words on the subject...

The Chef Has Imagination or It's Too Hard to Do it Easy
by Ogden Nash, 1949

Hark to the lettuce lover.
I consider lettuce a blessing.
And what do I want on my lettuce?
Simply a simple dressing

But in dining car and hostel
I grow apoplectic and dropsical;
Is this dressing upon my lettuce,
Or is it a melting popsicle?

A dressing is not the meal, dears,
It requires nor cream nor egg,
Nor butter nor maple sugar,
And neither the nut nor the meg.

A dressing is not a compote,
A dressing is not a custard;
It consists of pepper and salt,
Vinegar, oil, and mustard.

It is not paprika and pickles,
Let us leave those to the Teutons;
It is not a pinkish puddle
Of grenadine and Fig Newtons.

Must I journey to France for dressing?
It isn’t a baffling problem;
Just omit the molasses and yoghurt,
The wheat germ, and the Pablum.

It’s oil and vinegar, dears,
No need to tiddle and toil;
Just salt and pepper and mustard,
And vinegar, and oil.

For Brillat-Savarin, then, and Hoyle
Stick, friends, to vinegar and oil!
Yachtsman, jettison boom and spinnaker,
Bring me oil and bring me vinegar!
Play the music of Haydn or Honegger,
But lace it with honest oil and vinegar!
Choir in church or mosque or synagogue,
Sing, please, in praise of oil and vinegogue.
I’m not an expert, just a beginneger,
But I place my trust in oil and vinegar.
May they perish, as Remus was perished by Romulus,
Who monkey with this, the most sacred of formulas.