1. Cream butter and sugar together; then add egg yolk and beat well.

2. Sift dry ingredients, and add to creamed mixture, from step 1, along with milk and vanilla.

3. Divide dough in half.

4. Add chocolate to one part, and chill the dough in the refrigerator.

5. Pat each part of dough into a thin, oblong sheet.

6. Place the chocolate dough over the white dough.

7. Roll tightly, and chill in the refrigerator until firm.

8. Slice into thin cookies.

9. Bake on a greased cookie sheet in the oven at 375 degrees, for 10 minutes.

Note:
You may want to ask an adult how to separate an egg to get just the yolk.