Sift flour, baking soda, salt, and cinnamon in a mixing bowl. Add rolled oats and mix to incorporate. Set aside.
In a separate bowl, Tip in butter, brown sugar, granulated sugar then beat until creamy. Add vanilla extract and egg then beat again until well incorporated.
Fold-in the flour mix into wet ingredients in three batches until no traces of flour is left and dough forms. Chill in the fridge for a minimum of 30 minutes or overnight.
Pre heat oven at 170°C/338°F and line baking sheet with parchment paper.
Remove cookie dough from the refrigerator and weigh 60 grams of dough. Roll into balls and arrange in the baking sheet. Lightly flatten the cookie dough balls a bit with a spoon or palm of your hand.
Bake in pre heated oven for 10 - 13 minutes at 170°C/338°F or when the sides of the cookies are golden and the middle is a bit soft. Remove from the oven and let it rest for 5 to 10 minutes before transferring to a cooling rack. Bon appetit!