Preheat oven to 350℉
Cream 1 cup butter or margarine, softened and 2 Cups brown sugar, lightly packed in the bowl of a stand mixer fitted with the paddle attachment. (You can also use a large bowl and a hand mixer.) Cream until smooth, about 1-2 minutes.
Add eggs, one. at a time and beat, add1 tsp vanilla extract
In another bowl combine, 2 Cups all-purpose flour, 1 tsp cinnamon, 1 tsp Baking powder, ½ tsp Baking Soda, ½ tsp salt, 2 cups rolled oats
Add the dry ingredients into the wet ingredients and combine being careful not to overmix, add the raisins (or mix-in of your choice), stir to incorporate
chill the dough for 30 minutes
Drop by heaping Tbsp to a prepared baking sheet or lined with parchment
Bake for 10-12 minutes just until the base starts to turn golden brown (the tops will lose that glossy look once baked)
cool on the sheet pan for 5 minutes, then transfer to a cooling rack to cool completely
Store in an air-tight container for up to 4 days, or freeze for up to 3 months.