Preheat the oven to 350°F.

In a large bowl, using either a KitchenAid mixer or hand-held mixer, cream together the brown sugar with the butter and shortening.

Add the egg yolk.

Then add the vanilla extract.

Combine the flour and salt together and slowly add it to the butter mixture.

Mix until the dough comes ccompletely together.

Shape dough into balls.

Roll in egg white, then walnuts.

Place the cookies on cookie sheets about 2 inches apart.

Make an indentation in each cookie using a melon scoop.

Chill the cookies for at least 30 minutes before baking.

Bake in a preheated 350°F oven for about 15 minutes or until the cookies are set.

Remove the tray from the oven and indent them again, if you need to.

Fill the cookies with a little bit of jam.

Cool completely before serving.