Cookie Dough: Combine butter or margarine, brown sugar, egg and vanilla; beat until creamy. Sift flour, baking soda and salt, gradually adding to sugar mixture. Cover and store in refrigerator while preparing filling.
Filling: Mix walnuts, brown sugar and sour cream until creamy.
Cookie preparation: Shape cookie dough into 1-inch balls and place on lightly greased cookie sheet, leaving 1 1/2 inches between each cookie to allow spreading. Make a depression in the center of each cookie and spoon in filling.
Bake in preheated 350 degrees F oven for 10 minutes.