Preheat oven to 350 degrees and line two baking sheets with parchment paper.
In mixer combine sugars, butter and shortening. Mix until fluffy. Add eggs one at a time, mixing well after each addition. Mix in vanilla.
In small bowl combine dry ingredients and mix well. Add to butter mixture 3/4 cup at a time. Mixing well after each addition and stopping to scrape sides as needed. When thoroughly combined add chocolate chips.
Drop by measured teaspoonful onto lined cookie sheets and bake 8 minutes. After 8 minutes remove from oven and let stand on cookie sheet for one minute before moving to wire rack to finish cooling. This step is important for the cookies to firm up.