Preheat oven to 375. In a large bowl beat butter with an electric mixer on medium to high speed for 30 sedans. Add brown sugar, granulated sugar, baking powder, cinnamon, baking soda, and salt. Beat until combined, scraping side of bowl as needed. Beat in eggs and vanilla until combined. Add the flour and beat as much as you can with the mixer, then use a wooden spoon to stir in any remaining flour. Stir in oats, cranberries/raisins and walnuts, if using.