You can substitute jam for the red and green cherries but don't fill the centres until just before serving.
- Portion size 24 servings
In large bowl, cream together butter and sugar until light and fluffy. Beat in egg yolk and vanilla. Combine flour with cocoa; gradually blend into creamed mixture. Cover and chill for 30 minutes.
Shape dough into 1-inch (2.5 cm) balls. Dip in lightly beaten egg white; roll in walnuts. Place on ungreased baking sheets. Using finger or greased thimble, make indentation in centre of each ball. Bake in 325°F (160°C) oven for 7 minutes. Remove from oven and make indentations once more. Bake for 10 minutes longer or until set. Let cool on wire racks. Place cherry on each cookie.