Heat oven to 350°F. Lightly spray 9-inch round cake pan with nonstick cooking spray. Place margarine in sprayed pan; heat in oven for about 1 minute or until melted. Stir in 1/3 cup brown sugar until well mixed; spread evenly in pan. Top evenly with apple slices.
In large bowl, combine 2/3 cup brown sugar, apple butter and eggs; mix until well blended. Lightly spoon flour into measuring cup; level off. Add flour, baking powder, salt and apple juice; mix well. Pour batter over apples in pan.
Bake at 350°F. for 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes. Invert cake onto plate; remove pan. Cool at least 10 minutes.
Meanwhile, in small saucepan, combine half-and-half and cornstarch; blend well. Cook over medium-low heat, stirring constantly, until very hot and slightly thickened. Remove from heat.
In small bowl, beat egg yolk slightly. Gradually blend in sugar and vanilla; mix well. Slowly stir about half of hot mixture into egg mixture. Add egg mixture to hot mixture in saucepan; cook over medium-low heat, stirring constantly, just until thickened and bubbly around edges. (Mixture should coat back of metal spoon.) Cool slightly. Serve warm sauce over cake wedges.