Bring milk, butter, and half of sugar to a simmer in a heavy saucepan.
Beat remaining sugar, eggs, egg yolk, and cornstarch at medium-low speed with an electric mixer until blended. Slowly pour half of hot milk mixture into egg mixture, beating at low speed. Beat in remaining hot mixture. Cook over medium heat about 5 minutes or until mixture thickens. (Do not boil.)
Remove from heat, and stir in yogurt. Divide mixture into 2 portions.
Process 1 mango in a blender until smooth. Stir into 1 portion of yogurt mixture. Cover and chill. Slice remaining mango. Cover and chill.
Stir lime juice into second portion of yogurt mixture. Cover and chill.
Cut pound cake into 12 slices, and spread jam on 1 side of each slice.
Place 2 tablespoons mango mixture and 2 tablespoons lime mixture into each of 6 (1 1/2-cup) parfait or wineglasses. Top each with 1 cake slice.
Arrange strawberry slices around inside of glasses. Add 3 tablespoons mango mixture and remaining cake slices. Arrange mango slices around glasses, and top with 3 tablespoons lime mixture.
Beat whipping cream with an electric mixer until foamy. Gradually add sugar, beating until stiff peaks form. Pipe or dollop whipped cream on top of parfait. Chill parfaits 2 to 6 hours. Garnish, if desired.