Beat butter, sugar, egg and vanilla extract in a bowl with electric mixer until smooth. Stir in sifted flour mixture. Add chocolate chunks and mix well.
Drop level tablespoons of mixture about 5 cm apart on baking paper lined oven trays. Bake for 12 minutes or until the top look just set. They will get firmer as they cool. Stand cookies 2 minutes before lifting onto a wire rack to cool.
Note - Sift together the flour, cocoa powder, baking soda and salt.
I used hershyey's natural unsweetened cocoa and Lindt dark chocolate 60% in this recipe.