Preheat the oven to 175°C
In a large bowl, put together the butter, brown sugar, egg and the vanilla extract until you get a smooth mixture.
In a separate bowl, whisk the flour, baking powder, cinnamon and salt.
Then fold the dry ingredients into the sugar-butter mixture. Stir in the raisins, walnuts and oats.
It depends on how you prefer your cookies but if you like them thick and chewy, chill the dough in the fridge for a bit before forming the cookies on your sheet.
The baking time needed for your cookies depends on your oven and on how long you chilled the dough. In general you should bake them for 10 to 12 minutes.
Take them out when golden at the edges but still a little undercooked-looking on top.
Let them sit on the hot baking sheet for 3-4 minutes before you transferring them to a plate.
Enjoy!!!