Walnut Thumbprints

In a large bowl, cream the butter and brown sugar until light and fluffy. Beat in egg and vanilla. Combine the flour, baking soda and salt; gradually add to the creamed mixture and mix well. Refrigerate for 30 minutes. , Roll into 1-in. balls. Place 2 in. apart on greased baking sheets. Using the end of a wooden spoon handle, make an indentation in the center of each ball. , Combine filling ingredients; spoon about 1 teaspoonful into each cookie. Bake at 350° for 11-13 minutes or until lightly browned. Cool for 5 minutes before removing to wire racks.