Cream together butter and sugar until light and fluffy. Blend in egg and vanilla. Add flour, baking soda, and salt and mix well. Drop by teaspoonful onto lightly greased cookie sheet. Make a well in center of each cookie.
Filling: 1 c. finely chopped walnuts; 1/2 c. brown sugar, 1/4 c. sour cream
To prepare filling, combine all ingredients and stir until well mixed. Spoon 1 tsp. filling into well of each cookie. Bake at 350 degrees for 10 - 12 minutes or until golden brown. ENJOY!!