MEATBALLS: Mix all ingredients, adding beaten egg whites last. Form
into balls. SAUCE: Boil first 6 ingredients 30 minutes. Strain; bring
to boiling point, add meat balls and simmer 15 minutes. Remove meat
balls to hot platter, keeping them hot. Add vinegar to liquid.
Dissolve flour in small amount of cold water, add to beaten yolks.
Add this thickening mixture gradually to seasoned liquid, stirring
constantly until smooth and thick; pour over meat balls and garnish
with lemon slices and capers.