Preheat oven to 190°C (375°F). Line two or three (in my case) baking sheets with parchment paper or with silicon mats. Set aside.
In a small bowl combine flour, baking soda, baking powder, cinnamon and salt. Set aside.
In another bowl blend together softened butter, white granulated sugar and brown sugar until well combined.
Add an egg, beat on medium speed until fluffy and light in color. This may take take between 30 seconds and 2 minutes.
Add the prepared dry ingredients into the mixture and blend on low speed until just combined.
Add oatmeal and beat on low speed until just combined.
If you plan to add anything else, like chocolate, raisins or anything else, this is the time to do it. I made three kinds, plain cookies, with chocolate chips and with raisins. If you are using just one add in, you can add to the whole batch, if using different, then split the prepared batter into equal parts and mix in the add ins. Using a tablespoon or an ice-cream scoop, take about two tablespoons of dough and roll into a ball. Place onto the prepared baking tray. Repeat with the remaining dough, placing the cookie balls about 3-4 cm apart.
Bake in the preheated oven for 8-10 minutes, or until the top is just set.
Allow the cookies to cool on the baking tray about 5-10 minutes, before moving them to the wire rack to cool completely.
Enjoy!