Grease an 8-inch spring-form pan and set aside.
Mix the chopped hard-boiled eggs and mayonnaise to make an egg salad. Evenly
spread it into the bottom of the spring-form pan and cover with a layer of chopped onion. Stir
together cream cheese and sour cream until smooth and spread over the onion layer. Wrap the pan in
cellophane and chill for at least three hours in
the refrigerator (but it can stay overnight).
Once completely chilled,
unwrap the pan and spread the caviar over the top. Run a knife around the edge of the pie
and remove the side of the spring-form pan. Garnish with lemon wedges and
parsley sprigs before serving. Serve with baguette rounds or other bread on
which people will spread the caviar pie.