In a large mixing bowl, cream butter, shortening and brown sugar until fluffy, about 3 minutes. Add eggs, beating well after each addition. Beat in vanilla. Scrape down bowl. Turn mixer on low and gradually add in dry ingredients. Mix only until flour disappears. In necessary, turn off mixer and finish mixing with a wooden spoon. Wrap dough in plastic wrap and refrigerate for at least one hour.
Preheat oven to 350 F. Line baking sheets with parchment paper. Use a cookie scoop to measure out dough into 1? balls. Roll in your hands and place on baking sheets. Bake for 8-10 minutes (mine were 9 1/2 minutes). Slide parchment onto a cooling rack for 5 minutes, then remove cookies from parchment to rack to cool completely.
Variation: Simply add any flavor chocolate chips (I used peanut butter and milk chocolate swirls) and use a cookie scoop to measure out, do not roll in your hands. Bake 10 minutes.