In the bowl of a stand mixer fitted with the paddle attachment (or using a hand mixer and large bowl), cream the butter and sugar together until pale and fluffy.
Scrape the bowl down then add the eggs, one at a time. Beat well after each addition and scrape the bowl down to make sure all the ingredients incorporate well.
Add the vanilla and mix in. Sift together the flour, baking powder, baking soda, cinnamon and salt.
Add the dry ingredients to the wet ingredients along with the rolled oats and mix on low speed until just combined. Avoid over-mixing as this will result in tough cookies.
Scoop the dough onto baking sheets lined with parchment paper using a ice cream scoop or tablespoons. Space them a few centimeters apart to give them some room while they bake and spread. Place in the refrigerator and allow to chill for 15 minutes.
Preheat the oven to 180°C/350°F.
Remove the cookie dough from the fridge and place into the oven.
Allow to bake for 7-10 minutes until golden brown with crisp edges.
Remove from the oven, transfer to a wire rack and allow to cool.