In a large bowl, cream the butter and cream cheese until light and fluffy. Add egg yolks. Combine flour and baking powder; gradually add to the creamed mixture and mix well. Cover and chill overnight.
In a small bowl, combine filling ingredients (mixture will be thick). Divide dough into fourths (dough will be sticky). On a well-sugared surface, roll out each portion into a 12-in. x 10-in. rectangle. Cut into 2-in. squares. Place about 1 teaspoon filling in the center of each square. Fold over two opposite corners; seal tightly.
Place 2 in. apart on ungreased baking sheets. Bake at 350° for 15-18 minutes or until lightly browned. Remove to wire racks to cool.