In a bowl, beat the sugar and milk until it dissolves. Add peanut butter, vanilla and incorporate very well.
Add the oats, oat flour, baking soda, salt and fold them in. Do not over-mix, just make sure there are no flour lumps.
Pop the dough in the fridge for 15 minutes.
Preheat the oven to 180°C (355°F).
Divide the dough into 9 parts and place them on a non-stick baking sheet or a silicone mat/parchment paper, you can use an ice cream spoon to scoop them out. Make sure to leave a bit of space between the cookies because they will expand a little.
Lightly press the cookies and optionally add some peanuts on top as decoration.
Bake for 20 minutes or until cookies are light golden brown. Turn the oven off and let the cookies sit inside for 8-12 minutes.
Take the tray out of the oven and let them cool completely before removing the cookies. It is important to allow them to reach room temperature so that they can harden.
Store them in an airtight container in a cool place or in the fridge.