Cream together the butter, sugar, and vanilla.

Add the egg and beat until fluffy.

In a separate bowl, sift the dry ingredients. Then stir them into the butter mixture.

Divide the dough in half. Put one half in a second bowl and mix in the melted chocolate.

Cut four pieces of wax paper, 8" x 12" each.

Roll the chocolate dough between two of the pieces of wax paper and the white dough between the other two pieces. Roll the dough to the very edges of the wax paper.

Remove the top sheets of paper and turn the white layer onto the chocolate layer.

Remove the paper from the white layer and trim the edges.

Starting at the wide edge, roll both of the layers together like you would for a jelly roll, removing the wax paper from the chocolate layer as you roll.

Wrap the roll in wax paper and chill until firm (about 1 hour). If you're going to leave it in the refrigerator longer than 2 hours, also cover the roll in plastic wrap so it doesn't dry out.

About 10 minutes before removing the cookie dough roll from the refrigerator, preheat the oven to 375℉ and grease a cookie sheet or line with parchment paper.

Remove the cookie dough roll from the refrigerator. Slice the roll with a very sharp knife. Each cookie should be about ⅜" thick.

Bake on a greased cookie sheet at 375℉ for 10 minutes or until lightly browned.