Paula's Chocolate Shortbread Cookies

I made these for the first time last December, and Lei and I snuck them into a showing of "Sherlock Holmes." They are light and not too rich, so if you want a chocolate-y treat that doesn't make you feel like death afterward, these are your friends.

CHOCOLATE SHORTBREAD COOKIES
1 c. butter at room temperature
1 c. sugar
6 T. cocoa powder
1 t. vanilla
1 1/2 c. flour
2 T. cornstarch
1/4 t. salt
2/3 c. finely chopped walnuts (optional, I left these out, but I'm sure they'd be good)

Cream butter. Add sugar and cocoa. Cream until light. Add vanilla. Sift flour, cornstarch and salt together. Stir in nuts, if using. Mix into creamed mixture. Drop by rounded teaspoons onto a greased cookie sheet. Bake at 325 degrees 20-30 min. Don't over-bake. Cool 10-15 minutes before removing to wire rack.