Preheat oven to 350 degrees and line two baking sheets with parchment.
In the bowl of an electric mixer, beat the butter until light and fluffy. Add the brown sugar and granulated sugar, continue beating until fluffy.
Turn the mixer to low and stir in the eggs, one at a time, until incorporated thoroughly. Add the vanilla and stir.
In a medium bowl, sift together the flour, baking powder, cinnamon and salt. Gradually add the dry ingredients to the mixer bowl and stir to combine. Stir in the oats and raisins.
Using a cookie scoop or tablespoon, place 2 inch mounds of dough on the prepared baking sheets leaving a couple inches in between because they will spread.
Bake in a 350 degree oven for 15 - 17 minutes or until golden brown. Cool for a couple minutes on the baking sheet and then transfer to a wire rack to cool completely.
Store in an airtight container.
Notes
Oatmeal Raisin Cookie dough can be made up do 24 hours in advance and stored in the refrigerator covered with plastic wrap.To make puffier, more cake like cookies, replace the baking soda with 1 1/2 tablespoons baking powder and proceed as instructed.