Measure out oil in advance.
Crack the egg and separate white from yolk. Put the egg yolk into a large bowl.
By hand, whisk together the egg yolk and mustard.
Very, very slowly add a few drops of oil to the egg yolk mixture and whisk. (Get a friend to help pour)
Repeat pouring drops and whisking. Work up to adding a bit more oil at a time, but do this gradually so you don't break the emmulsion.
When all the oil is incorporated, add vinegar/lemon juice.
Taste and add salt, pepper, more lemon juice to taste.
Can add other spices at this point if you like something different.
Chill in refrigerator overnight. Use within 1 week.
