Sift dry ingredients: flour, baking powder, baking soda and cinnamon(optional)
Line baking sheets with parchment paper
Pre-heat oven to 375F
With your mixer at low-speed, cream butter, sugar and salt. At this stage it is important to watch the consistency of the butter and sugar. Light and fluffy will yield to lighter cookies. For denser cookies, mix just until well blended.
Still mixing at low-speed, add the eggs gradually making sure to scrape the sides and bottom of the bowl with every addition.
Combine the oats with the dry ingredients and add to the butter mixture. Mix until combined without over-mixing. Stir in the raisins.
Use spoons (you'll need 2 because: one for scooping batter, the other to aid when you're dropping the batter on the pan) or use an ice cream scoop with a spring release to drop batter into to the prepared baking sheets. Make sure to leave space in between.
Bake for about 10 - 12 minutes.
If you want to add walnuts/pecans to a small portion of the batter. Set aside about a quarter of the batter and fold in 1/2 cup of walnuts/pecans.