1 cup butter 1 cup white sugar 1/2 cup brown sugar 2 large eggs 1/2 T cream of tartar 1 tsp baking soda 1/2 tsp salt 1/2 tsp vanilla 1/2 tsp cinnamon 2-2 3/4 cups flour Equal parts cinnamon and sugar for rollingUsing a stand or electric mixer, cream together butter and sugars till light and fluffy. Add all the dry ingredients except the flour and mix well. Add the eggs and mix well, scraping down the sides and bottom of the bowl several times. Add 2 cups of flour and mix just until incorporated. Add the additional 3/4 cup as needed to form a smooth, soft dough. Do not over mix. Cover and refrigerate for 1 hour. Scoop 2 T-sized portions and roll into smooth balls, then roll in the cinnamon/sugar mixture to coat. Place on parchment-lined cookie sheet, spaced 2 inches apart. Bake at 350 degrees for 12 minutes or until set.