Blend the eggs and mayonnaise (using enough mayonnaise just to bind the eggs) in a small bowl. Line a well-buttered 8 or 9-inch pie pan with the egg mixture, pressing firmly over the bottom and up the sides to form the crust. Scatter the scallions over the crust, then spread with the caviar. Frost with the sour cream and refrigerate until ready to serve. Set the caviar pie on a cocktail table with crackers or freshly made melbas, which can be dipped or spread.;