In a small bowl, combine the flour, baking powder and salt; set aside. In a large bowl, cream butter and brown sugar until light and fluffy. Beat in eggs and vanilla. Gradually add dry ingredients; mix well. Spread two-thirds of the batter into an ungreased 13x9-in. baking pan. Top with apples; set aside.
In a small bowl, beat cream cheese, sugar and egg yolk until smooth. Spoon over apples. Drop remaining batter by teaspoonfuls over top. Bake at 350° for 25-30 minutes or until golden brown.