Cream butter and white and brown sugar together thoroughly. Add egg and vanilla and beat until fluffy. Sift dry ingredients together. Stir into butter mixture with a wooden spoon. Drop with a 2 oz. scoop onto parchment lined baking sheets. Bake at 350 for 10 - 12 minutes rotating pans halfway through. Cookies should be browned on edges and still light in the middle for a chewy cookie.