Heat oven to 350 Fahrenheit.
Wet ingredients. In a bowl of stand mixer with the paddle attachment beat the butter, both sugars until creamy (medium speed). About 2 minutes.
Add egg, vanilla extract to the butter mixture and beat again on low.
Dry ingredients. In a medium bowl whisk together sifted flour, oats, sifted baking soda, sifted baking powder, salt, mix well and set aside.
Add the dry ingredients in batche to the wet ingredients until thoroughly combined. Stir in raisins.
Freeze the dough for 10–15 minutes until it feels like soft playdough. You can skip chilling if needed, but the cookies will spread more and may bake unevenly. The flavor will stay the same.
Roll into 12–13 balls (about 2 tablespoons each) and place on baking trays. Leave 2 inches apart. For thinner cookies, use less dough and bake slightly less time.
Bake for 10-12 minutes until they start turning golden brown. Let rest in a pan for 10 minutes and transfer to a wire rack to continue to cool.
Once the oatmeal cookies are completely cooled (although they are very delicious when warm too) serve them with a tall glass of milk on the side.