(adapted from The Joy of Cooking)

This one takes a little time, but is well worth it.

Boil the potatoes until just tender – don’t overcook. Slice or chop them the way you like. In the fridge, marinate well in a mixture of 1⁄4 t. salt, 1⁄4 t. pepper, 1⁄4 cup olive oil, 2 T. vinegar or lemon juice, 1 chopped clove of garlic.

Add a mixture of any of the following:
Chopped hard boiled eggs, spring onions, celery, cucumbers, parsley, olives, pickles, capers
1 T salt
Paprika to taste
Refrigerate for an hour.
(at this point you can serve it if you like)

In the meantime, dissolve 1⁄2 t. dry mustard, 1-2 T sugar, 1⁄2 t. salt, 2 T. flour, 1⁄4 t. paprika in 1⁄2 cup of water.
In the top of a double boiler beat 1 egg OR 2 yolks and 1⁄4 c. vinegar. Add the dissolved ingredients and cook over boiling water, stirring regularly, until thick. Add 2 T. butter and cook until incorporated.

Chill the dressing before adding it to the potatoes. Place the complete mixture in the fridge for at least one hour before serving. Garnish with freshly chopped parsley.