Mayonnaise

This is a good lesson for teaching children about "emulsions".  Mustard and egg yokes contain lecithin which is an essential element in creating the emulsion in mayonnaise.  Eggs loose lecithin as they age, so using fresh eggs is important.  See this Good Eats Fan Page for more details.

½ teaspoon sugar
½  teaspoon powdered mustard
¾ teaspoon salt
 1 fresh egg
 2 tablespoons lemon juice
 1 cup vegetable oil

Blend sugar, mustard, salt, egg and 1 tablespoon lemon juice in blender or food processor.  Add 1 tablespoon oil and process at highest speed, then add 1 more tablespoon of oil and process again.  With blender or food processor, running pour a slow, steady stream of oil through the food tube or hole in lid until all is used.  When very thick add the last tablespoon of  lemon juice and process again.  Store in the refrigerator in an air tight container.  Discard any unused portion after about a week.

If you pour the oil too rapidly, the emulsion will not set up properly.   Here is a trick if your mayonnaise turns out too soupy. Scrape it out into a bowl and reserve for later.  Put another egg in the blender or food processor with two tablespoon of the mayonnaise and process again from the beginning using the remainder of the mayonnaise.