Place half cake cubes in bottom of 2-quart clear glass bowl.
Moisten with some of the sherry. Cover with jam. Top with remaining cake cubes.
Add enough additional sherry to moisten cake well. In saucepan beat eggs and egg yolk.
Stir in milk and granulated sugar. Cook and stir until custard coats a metal spoon. Remove from heat.
Cool at once in ice water; stir occasionally. Spoon cooled custard over cake.
Beat egg white to soft peaks. Gradually add powdered sugar, beating until stiff peaks form. Whip cream with vanilla. Fold in egg white. Pile mixture atop custard.
Refrigerate 6 hours or overnight. Garnish with slivered almonds.
