In a large bowl, cream shortening and brown sugar until light and fluffy. Beat in egg and vanilla. Combine the flour, baking powder and salt; gradually add to creamed mixture and mix well.
Shape into 1-in. balls. Place 2 in. apart on ungreased baking sheets. Using the end of a wooden spoon handle, make a 1/2-in.-deep indentation in the centre of each ball. Combine filling ingredients; spoon into cookies.
Bake at 350° for 9-11 minutes or until lightly browned. Cool for 1 minute before removing from pans to wire racks. If desired, top with frosting.