Preheat oven to 300˚F (150˚C). Grease cookie sheets. Separate egg, slightly beat egg-white using a fork; set aside. Cream butter, brown sugar and egg yolk. Beat in vanilla extract until combined. Add flour and salt, mixing well. Shape dough into 1" inch balls. Roll in egg white, then in walnuts. Place on cookie sheets about 2 inches apart. Bake for 5 minutes. Remove cookies from oven. With thumb, indent each cookie. Spoon about 1/2 teaspoon aroniaberry jam in thumbprint. Return to oven for another 10 minutes or until cookies are slightly firm around the edges. Transfer to wire rack to cool completely. *Use the recipe for homemade aroniaberry jam found in the breakfast recipe section.