Melt chocolate morsels in a double boiler. Set aside.
Sift flour, cocoa, baking soda and salt into medium bowl.
Beat butter, brown sugar and granulated sugar in large mixer bowl until creamy.
Add melted chocolate and mix well.
Add egg and vanilla extract, mixing until well blended, about 1 minute.
Add flour mixture in 2 to 3 batches. Mix until just blended.
Place batter in fridge for 60 minutes to overnight. (This is the mistake that changed this cookie recipe).
Mixture should be really hard. If not, put it back in the fridge until it becomes stiff.
Place bowl in a microwave and reheat in short intervals until the dough becomes malleable.
Pour into a cake tin (I used a tinfoil pan).
Preheat oven to 325 degrees.
Bake for 25 to 28 minutes or until toothpick inserted in center comes out clean. Cool on baking sheets for 5 minutes. Remove to wire rack to cool completely.