Beat butter in large mixer bowl until smooth. Add brown sugar and vanilla extract; beat until fluffy. Add eggs, one at a time; beating until mixture becomes lighter in color. Alternately add flour mixture and cocoa mixture to bowl, mixing after each addition until combined. You will use the flour 3 times and cocoa mixture twice. Stir in morsels. Drop batter by level tablespoon measure about 2 inches apart onto prepared baking sheets. Press batter down lightly to even out. You will need 54 total for the pies.