Thumbprint Cookies with Icing

Cookies: Beat the 2 egg yolks with the vanilla. Cream in the shortening, butter, and brown sugar. In separate bowl, mix the flour and salt together. Then slowly add to the first bowl. Roll batter into small balls. Dip the balls into egg whites and then roll in the walnuts. Place on cookie sheet and make indent with your thumb. Bake at 350 for approximately 13 minutes. Let cool. Icing: Melt butter and add a splash of milk and a few drops of food coloring. Mix in powdered sugar until it barely drips off of spoon. Variation: Instead of food coloring, add a tsp of powdered cocoa (more or less to taste) for a mild chocolate flavored icing. Put icing into indent in cookies. Refrigerate.