In a large bowl, cream the butter. Add the sugar; mix until light and fluffy. Beat in eggs and vanilla. Combine the flour, baking soda, cinnamon, baking powder, and salt in a medium bowl; gradually add to creamed mixture and mix well. Stir in oats. (Don't skimp on the oats and be sure to mix evenly!),
Shape into 1-in. balls. Place 2 inches apart on uncreased baking sheets. Bake at 350 for 6-8 minutes or until golden brown. Cool for 1 minute before removing to wire racks (Note: Bigger cookies tend to end up thinner. If there are any parts with no oats, they will be very thin. Also do not place dough on warm pan!). Yield: 4 doz.