Press the egg yolks through a sieve and mix them with 2 tablespoons of mayonnaise.
Preferably, spread the yolks on the bottom of four small ramekins. Second choice is one 8-ince pie plate.
Using a food processor, mix the cream cheese, mayonnaise, and 1 tablespoon of sour cream.
Spread the cream cheese mixture over the egg mixture.
Spread a thin layer of sour cream over the top of the cream cheese mix, then a layer of onion.
Now, spread a layer of caviar on the top.
Garnish with lemon slices.
Serve this delicious, but simple, appetizer with toasted French bread.