Combine the egg yolks and condensed milk
in a double boiler. Add lemon zest.
Cook over medium heat, stirring
constantly, until very thick and mixture coats the back of a spoon when
lifted, about 30 minutes. Chill for 1 hour for easier handling.
Grease hands and shape egg mixture into
small balls, placing each ball into a greased pan.
In the saucepan, melt sugar and cream of
tartar over low heat. Do not stir, otherwise sugar will crystallize.
When the sugar becomes a brown syrup, stir then dip each ball into the
syrup with a pair of tongs, swirling to coat evenly. Keep the syrup over
low heat so it does not harden. Alternatively, if you do not wish to
coat the ball in syrup, dust them lightly with sugar.
Put each coated ball into a greased pan
and set aside to cool. Wrap individually in cellophane, if desired,